Instant-runoff voting: Difference between revisions
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Undid revision 1265061559 by The Smartest Prize (talk) no, a majority-first-place winner will always be selected. Condorcet is more subtle than that and should be phrased less ambiguously. |
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{{Short description|Single-winner ranked-choice electoral system}} |
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{{Use dmy dates|date=November 2012}} |
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{{for|the proportional electoral system applying ranked ballots to multi-member constituencies|Single transferable vote}} |
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[[File:Preferential ballot.svg|right|thumb|Example instant-runoff voting ballot]] |
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{{for|ranked methods in general|Ranked voting}} |
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{{Electoral systems}} |
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{{Use dmy dates|date=April 2024}} |
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{{Use American English|date=May 2024}} |
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{{Electoral systems sidebar|expanded=Single-winner}} |
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'''Instant-runoff voting''' ('''IRV''') ({{abbr|[[American English|US]]:|United States and Canada|style=font-size:85%}} '''ranked-choice voting''' ('''RCV'''), {{abbr|[[Australian English|AU]]:|Australia|style=font-size:85%}} '''preferential voting''', {{abbr|[[British English|UK]]:|United Kingdom and New Zealand|style=font-size:85%}} '''alternative vote''') is a [[single-winner]], [[Sequential loser method|multi-round elimination rule]] that uses [[ranked voting]] to simulate a series of [[Runoff (election)|runoff]]s with only one vote. In each round, the candidate with the fewest votes counting towards them is eliminated, and the votes are transferred to their next available preference until one of the options reaches a majority of the remaining votes. Instant runoff falls under the plurality-with-elimination family of voting methods,<ref>{{Cite journal |last=Nurmi |first=Hannu |date=June 2005 |title=Aggregation problems in policy evaluation: an overview |url=http://dx.doi.org/10.1016/j.ejpoleco.2004.08.001 |journal=European Journal of Political Economy |volume=21 |issue=2 |pages=287–300 |doi=10.1016/j.ejpoleco.2004.08.001 |issn=0176-2680}}</ref> and is thus closely related to rules like the [[exhaustive ballot]] and [[Runoff election|two-round runoff system]].<ref>{{Cite book |last1=Aubin |first1=Jean-Baptiste |url=https://hal.science/hal-04631154/ |title=A simulation-based study of proximity between voting rules |last2=Gannaz |first2=Irène |last3=Leoni-Aubin |first3=Samuela |last4=Rolland |first4=Antoine |date=July 2024}}</ref><ref>{{Cite journal |last1=Hyman |first1=Ross |last2=Otis |first2=Deb |last3=Allen |first3=Seamus |last4=Dennis |first4=Greg |date=2024-09-01 |title=A majority rule philosophy for instant runoff voting |url=https://link.springer.com/article/10.1007/s10602-024-09442-3 |journal=Constitutional Political Economy |language=en |volume=35 |issue=3 |pages=425–436 |doi=10.1007/s10602-024-09442-3 |issn=1572-9966}}</ref> |
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IRV has found some use [[History and use of instant-runoff voting|in national elections in several countries]], predominantly in the [[Anglosphere]]. It is used to elect members of the [[Australian House of Representatives]] and the [[National Parliament of Papua New Guinea]] as well as the [[President of India#Election process|President of India]], the [[President of Ireland]], and the [[President of Sri Lanka]]. |
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'''Instant-runoff voting''' ('''IRV'''), also known as the: '''alternative vote''' ('''AV'''), '''transferable vote''', '''ranked choice voting''', or '''preferential voting''' is an [[voting system|electoral system]] used to elect a single winner from a field of more than two candidates. It is a [[Ranked voting systems|preferential voting]] system in which voters rank the candidates in order of preference rather than voting for a single candidate. |
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The rule was first developed and studied by the [[Marquis de Condorcet]], who came to reject it after discovering it could eliminate the [[majority-preferred candidate]] in a race (today often called a [[Condorcet winner]]).<ref name=":034">{{Cite book |last=Condorcet |first=Jean-Antoine-Nicolas de Caritat |title=Complete Works of Condorcet |date=1788 |volume=13 |publication-date=1804 |pages=243 |language=fr |chapter=On the Constitution and the Functions of Provincial Assemblies |quote=En effet, lorsqu'il y a plus de trois concurrents, le véritable vœu de la pluralité peut être pour un candidat qui n'ait eu aucune des voix dans le premier scrutin. |chapter-url=https://books.google.com/books?id=d0cwAAAAYAAJ&q=Oeuvres%20de%20Condorcet,%20Volume%2013&pg=PA243}}</ref><ref name=":032">{{Cite journal |last=Nanson |first=E. J. |date=1882 |title=Methods of election: Ware's Method |url=https://archive.org/details/transactionsproc1719roya/page/206 |journal=Transactions and Proceedings of the Royal Society of Victoria |volume=17 |pages=206 |quote=The method was, however, mentioned by Condorcet, but only to be condemned.}}</ref><ref name=":22322323">{{cite journal |last1=Campbell |first1=D.E. |last2=Kelly |first2=J.S. |year=2000 |title=A simple characterization of majority rule |journal=[[Economic Theory (journal)|Economic Theory]] |volume=15 |issue=3 |pages=689–700 |doi=10.1007/s001990050318 |jstor=25055296 |s2cid=122290254}}</ref> IRV is known to exhibit other [[Pathological (mathematics)#In voting and social choice|mathematical pathologies]], which include [[Monotonicity criterion|non-monotonicity]]<ref>{{Cite journal |last1=Doron |first1=Gideon |last2=Kronick |first2=Richard |date=1977 |title=Single Transferrable Vote: An Example of a Perverse Social Choice Function |url=https://www.jstor.org/stable/2110496 |journal=American Journal of Political Science |volume=21 |issue=2 |pages=303–311 |doi=10.2307/2110496 |issn=0092-5853 |jstor=2110496}}</ref> and the [[no-show paradox]].<ref name=":05">{{Cite SSRN |last=Stensholt |first=Eivind |date=2018 |title=What is Wrong with IRV? |ssrn=3272186}}</ref><ref name="auto4">{{cite journal |last=Ray |first=Depankar |year=1986 |title=On the practical possibility of a 'no show paradox' under the single transferable vote |journal=Mathematical Social Sciences |volume=11 |issue=2 |pages=183–189 |doi=10.1016/0165-4896(86)90024-7}}</ref> Like some other commonly-used systems, IRV also exhibits a kind of [[Independence of irrelevant alternatives|independence of irrelevant alternative]] violation called a [[center squeeze]],<ref name=":73323">{{Cite journal |last=Nurmi |first=Hannu |date=December 1996 |title=It's not just the lack of monotonicity1 |url=http://www.tandfonline.com/doi/abs/10.1080/00344899608522986 |journal=Representation |language=en |volume=34 |issue=1 |pages=48–52 |doi=10.1080/00344899608522986 |issn=0034-4893}}</ref><ref name=":852423">{{Cite journal |last1=McGann |first1=Anthony J. |last2=Koetzle |first2=William |last3=Grofman |first3=Bernard |date=2002 |title=How an Ideologically Concentrated Minority Can Trump a Dispersed Majority: Nonmedian Voter Results for Plurality, Run-off, and Sequential Elimination Elections |url=https://www.jstor.org/stable/3088418 |journal=American Journal of Political Science |volume=46 |issue=1 |pages=134–147 |doi=10.2307/3088418 |issn=0092-5853 |jstor=3088418 |quote="As with simple plurality elections, it is apparent the outcome will be highly sensitive to the distribution of candidates."}}</ref> which may sometimes prevent the election of a Condorcet winner. Whilst the [[Marquis de Condorcet]] early on showed that it did not satisfy his [[Condorcet winner criterion]], which it may fail under certain scenarios, instant-runoff voting satisfies many other majoritarian criteria, such as the [[Majority favorite criterion|majority criterion]], [[mutual majority criterion]] and the [[Condorcet loser criterion]]. |
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Ballots are initially distributed based on each elector's first preference. If a candidate secures more than half of votes cast, that candidate wins. Otherwise, the candidate with the fewest votes is eliminated. Ballots assigned to the eliminated candidate are recounted and added to the totals of the remaining candidates based on who is ranked next on each ballot. This process continues until one candidate wins by obtaining more than half the votes. |
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Advocates have argued these properties are positive, because voting rules should encourage candidates to focus on their [[core support]] or political base, rather than building a broad coalition.<ref>{{Cite journal |last1=Hyman |first1=Ross |last2=Otis |first2=Deb |last3=Allen |first3=Seamus |last4=Dennis |first4=Greg |date=September 2024 |title=A Majority Rule Philosophy for Instant Runoff Voting |journal=Constitutional Political Economy |volume=35 |issue=3 |pages=425–436 |arxiv=2308.08430 |doi=10.1007/s10602-024-09442-3 |issn=1043-4062}}</ref> They also note that in countries like the [[United Kingdom]] without [[Primary election|primaries]] or [[Two-round system|runoff elections]], IRV can prevent [[Spoiler effect|spoiler effects]] by eliminating minor-party candidates in early rounds, and that unlike plurality, it is not [[Independence of clones criterion|affected by the presence of duplicate candidates (clones)]]. |
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IRV has the effect of avoiding split votes when multiple candidates earn support from like-minded voters. For example, suppose there are two similar candidates A & B, and a third opposing candidate C, with raw popularity of 35%, 25% and 40% respectively. In a [[plurality voting system]], candidate C may win with 40% of the votes, even though 60% of electors prefer either A or B. Alternatively, voters are pressured to choose the seemingly stronger candidate of either A or B, despite personal preference for the other, in order to help ensure the defeat of C. It is often the resulting situation that candidate A or B would never get to ballot, whereas voters would be presented a two candidate choice. With IRV, the electors backing B as their first choice can allocate their preferences as #1 for B and #2 for A, which means A will win despite the split vote in first choices. |
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== Election procedure == |
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Instant-runoff voting is used to elect members of the [[Australian House of Representatives]] and most Australian State Governments,<ref name="Australian Electoral Commission">{{cite web|url=http://www.aec.gov.au/ |title=Australian Electoral Commission |publisher=Aec.gov.au |date=2014-04-23 |accessdate=2014-04-30}}</ref> the [[President of India]], members of [[Vidhan Parishad|legislative councils]] in India, the [[President of Ireland]],<ref name="International Constitutional Law">{{cite web|url=http://www.servat.unibe.ch/icl/ei00000_.html|title=Ireland Constitution, Article 12(2.3)|publisher=International Constitutional Law|year=1995|accessdate=15 February 2008}}</ref> and the parliament in [[National Parliament of Papua New Guinea|Papua New Guinea]]. It is also used in Northern Ireland [[by-election]]s{{cn|date=May 2015}} and for electing [[hereditary peer]]s for the [[House of Lords|British House of Lords]].<ref name="Notice of House of Lords Conservative Hereditary Peers' By-Election Notice">{{cite web| author = House of Lords | authorlink = House of Lords | url = http://www.parliament.uk/documents/lords-information-office/holnotice20100601.pdf | title = House of Lords Website}}</ref> |
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[[File:IRV_counting_flowchart.svg|thumb|Flowchart of instant-runoff voting]] |
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In instant-runoff voting, as with other [[ranked voting]] rules, each voter orders candidates from first to last. The counting procedure is then as follows: |
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# If there is a candidate that has a majority of the top preferences of the valid, active ballots, then that candidate is elected and the count stops. If not, go to step 2. |
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The system is also used in local elections around the world: to elect the mayor in cities such as [[London]] in the United Kingdom (in the variant known as [[supplementary vote]])<ref name="The Supplementary Vote SV">{{cite web|url=http://www.electoral-reform.org.uk/article.php?id=58 |title=Electoral Reform Society - Supplementary Vote |publisher=Electoral-reform.org.uk |accessdate=17 April 2011}}</ref> and [[Dunedin]] and [[Wellington]] in New Zealand.<ref name="Elections - 2007 Final Results">{{cite web|url=http://www.wellington.govt.nz/haveyoursay/elections/results/2007/final/mayorfinal.html |title=Elections – 2007 Final Results |year=2007 |publisher=[[Wellington]] city council}}</ref> Variations of instant-runoff voting are employed by several jurisdictions in the United States, including [[San Francisco]],<ref name=mpr20090510/> [[San Leandro]], and [[Oakland, California|Oakland]] in [[California]];<ref name=or2010>{{cite web |url=http://oaklandrising.org/campaign/instant-runoff-voting|title=Oakland Rising:Instant Runoff Voting |publisher=oaklandrising.com |year=2010 |accessdate=23 December 2010}}</ref> [[Portland, Maine]]; [[Minneapolis, Minnesota|Minneapolis]] and [[Saint Paul, Minnesota|Saint Paul]] in Minnesota.<ref name=mpr20090510>[http://minnesota.publicradio.org/display/web/2009/05/10/instant_runoff_voting_excercises_election_judge_fingers/ "Instant runoff voting exercises election judge fingers"] Minnesota Public Radio, 10 May 2009</ref> The [[single transferable vote]], a multi-seat form of IRV, is used in [[Cambridge, Massachusetts]].<ref name=FairVoteWhere>{{cite web|title=Where Instant Runoff Is Used|url=http://www.fairvote.org/where-instant-runoff-is-used|work=Fair Vote|publisher=The Center for Voting and Democracy|accessdate=8 September 2013}}</ref> |
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# If there is more than one candidate left, eliminate the one with the fewest top preferences.{{efn|This procedure can be sped-up by eliminating more than one candidate if their combined top preferences are less than the next-lowest remaining candidate; this process is sometimes called batch elimination. When batch elimination is used, the procedure can terminate if some candidate has a majority.}} |
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# Reassign votes held by the eliminated candidate(s) to the highest available preference indicated on each ballot paper (setting aside any with no remaining preferences). Return to Step 1. |
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It is possible for a candidate to win an instant-runoff race without any support from more than half of voters, even when there is an alternative majority-approved candidate; this occurs when some voters [[Exhausted vote|truncate their ballots]] to show they do not support any candidates in the final round.<ref name=":1232">{{Cite SSRN |last=Dopp |first=Kathy Anne |date=2011 |title=Realities Mar Instant Runoff Voting Flaws and Benefits of IRV |ssrn=1858374}}</ref> In practice, candidates who do not receive a majority of votes in the first round usually do not finish with a majority.<ref name=":534">{{cite arXiv |eprint=2301.12075 |class=econ.GN |first1=Adam |last1=Graham-Squire |first2=David |last2=McCune |title=An Examination of Ranked Choice Voting in the United States, 2004-2022 |date=2023-03-06}}</ref> |
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It is used to elect the leaders of the [[Labour Party (UK)|Labour Party]]<ref>«[http://www.parliament.uk/briefing-papers/SN03938.pdf Leadership elections: Labour party]». Kelly, R., Lester, P., & Durkin, M. (2010). House of Commons Library Note, 6, pg. 12. Retrieved 14 November 2013.</ref> and the [[Liberal Democrats]] in the [[United Kingdom]] and was used in elections in [[Liberal Party of Canada leadership election, 2013|2013]] for the leader of the [[Liberal Party of Canada]]<ref name="Maclean's Explainer">{{cite web |url=http://www2.macleans.ca/2013/04/05/the-liberal-leadership-vote-who-what-where-when-how-could-it-go-wrong/ |title=What comes next in the Liberal vote |publisher=Maclean's |date=5 April 2013 |accessdate=6 May 2010}}</ref> and in Canada's [[New Democratic Party leadership election, 2012]]. |
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==Properties== |
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Many private associations also use IRV,<ref name="Organizations & Corporations">{{cite web |url=http://www.fairvote.org/?page=1964 |title=Organizations & Corporations |publisher=FairVote |date=17 March 2001 |accessdate=6 May 2010}}</ref> including the [[Hugo Award]]s for science fiction<ref name="Oscars Copy Hugos">{{cite web|url=http://www.thehugoawards.org/2009/09/oscars-copy-hugos/ |title=Oscars Copy Hugos |publisher=The Hugo Awards |accessdate=6 May 2010}}</ref> and the [[Academy of Motion Picture Arts and Sciences]] in selection of the Oscar for best picture.<ref name="www.oscars.org">{{cite web|url=http://www.oscars.org/press/pressreleases/2009/20090831a.html |title=Preferential Voting Extended to Best Picture on Final Ballot for 2009 Oscars |publisher=Oscars.org |accessdate=6 May 2010}}</ref> IRV is described in ''[[Robert's Rules of Order]] Newly Revised, 10th edition''.<ref name="autogenerated1">{{cite book|ref=harv|year=2000|pages=411–414|title=Robert's Rules of Order Newly Revised, 10th edition|isbn=978-0-7382-0307-2|publisher=Da Capo Press|last=Robert|first=Henry}}</ref> |
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=== Wasted votes and Condorcet winners === |
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Compared to a plurality voting system that rewards only the top vote-getter, instant-runoff voting mitigates the problem of [[Wasted vote|wasted votes]].<ref name="chamberlin23">{{cite journal |last1=Chamberlin |first1=John R. |last2=Cohen |first2=Michael D. |year=1978 |title=Toward Applicable Social Choice Theory: A Comparison of Social Choice Functions under Spatial Model Assumptions |journal=American Political Science Review |publisher=Cambridge University Press (CUP) |volume=72 |issue=4 |pages=1341–1356 |doi=10.2307/1954543 |issn=0003-0554 |jstor=1954543 |quote=A long-established response to the 'wasted vote' problem is the method advocated by Hare...}}</ref> However, it does not ensure the election of a [[Condorcet winner criterion|Condorcet winner]], which is the candidate who would win a direct election against any other candidate in the race. |
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===Invalid, incomplete and exhausted ballots{{Anchor|Exhausted ballots}}=== |
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==Terminology== |
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All forms of ranked-choice voting reduce to plurality when all ballots rank only one candidate. By extension, ballots for which all candidates ranked are eliminated are equivalent to votes for any non-winner in plurality, and considered [[exhausted ballots]]. |
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Instant-runoff voting derives its name from how ballot-count simulates a series of [[two-round system]] runoffs except that voter preference do not change between rounds.<ref name="publications.parliament.uk">{{cite web|url=http://www.publications.parliament.uk/pa/cm200001/cmselect/cmproced/40/4005.htm|title=Second Report: Election of a Speaker|date=15 February 2001|publisher=House of Commons Select Committee on Procedure|accessdate=18 February 2008}}<!--This ref describes similarities/differences between IRV and exhaustive ballot.--></ref> |
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Some political scientists have found the system contributes to higher rates of [[Spoiled vote|spoiled votes]],<ref name=":433">{{Cite SSRN |last1=Pettigrew |first1=Stephen |last2=Radley |first2=Dylan |date=2023 |title=Ballot Marking Errors in Ranked-Choice Voting |ssrn=4670677}}</ref> partly because the ballot marking is more complex.<ref name=":433" /><ref name=":534"/> Most jurisdictions with IRV do not require complete rankings and may use columns to indicate preference instead of numbers. In American elections with IRV, more than 99 percent of voters typically cast a valid ballot.<ref>{{cite web |date=1 August 2008 |title=Instant Runoff Voting and Its Impact on Racial Minorities |url=http://politicalreform.newamerica.net/files/irvracememo.pdf |archive-url=https://web.archive.org/web/20110615181347/http://politicalreform.newamerica.net/files/irvracememo.pdf |archive-date=15 June 2011 |access-date=15 August 2011 |publisher=New America Foundation}}</ref> |
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Britons and Canadians<ref>{{cite web|url=http://www.fairvote.ca/wp-content/uploads/2013/06/AV-backgrounder-august2009_1.pdf |title=The Alternative Vote: No Solution to the Democratic Deficit |publisher=Fair Vote Canada |accessdate=23 April 2014}}</ref> generally call IRV the "Alternative Vote" (AV). Australians, who use IRV for most single winner elections call IRV "preferential voting," as does [[Robert's Rules of Order]]. Americans in San Francisco, California, Portland, Maine and Minneapolis, Minnesota call IRV "ranked choice voting". IRV occasionally is referred to as Ware's method after its inventor, American [[William Robert Ware]]. |
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A 2015 study of four local US elections that used IRV found that inactive ballots occurred often enough in each of them that the winner of each election did not receive a majority of votes cast in the first round. The rate of inactive ballots in each election ranged from a low of 9.6 percent to a high of 27.1 percent.<ref>{{cite journal |last1=Burnett |first1=Craig M. |last2=Kogan |first2=Vladimir |date=March 2015 |title=Ballot (and voter) 'exhaustion' under Instant Runoff Voting: An examination of four ranked-choice elections |journal=Electoral Studies |volume=37 |pages=41–49 |doi=10.1016/j.electstud.2014.11.006 |s2cid=11159132}}</ref> |
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[[North Carolina]] law uses "instant runoff" to describe the contingent vote or "batch elimination" form of IRV in one-seat elections. A single second round of counting produces the top two candidates for a runoff election. |
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<ref>{{cite web|url=http://www.ncleg.net/enactedlegislation/sessionlaws/html/2005-2006/sl2006-192.html |title=S.L. 2006-192 |publisher=Ncleg.net |accessdate=6 May 2010}}</ref> Election officials in [[Hendersonville, North Carolina]] use "instant runoff" to describe a multi-seat election system that simulates in a single round of voting their previous system of multi-seat runoffs.<ref>{{cite web|url=http://blogs.citizen-times.com/blogs/index.php?blog=10&title=no_instant_runoff_in_hendersonville&more=1&c=1&tb=1&pb=1 |title=CITIZEN-TIMES: Capital Letters – Post details: No instant runoff in Hendersonville |publisher=Blogs.citizen-times.com |accessdate=6 May 2010}}</ref> State law in [[South Carolina]]<ref>{{cite web|url=http://www.scstatehouse.gov/sess116_2005-2006/bills/3720.doc |title=South Carolina General Assembly : 116th Session, 2005-2006 |publisher=Scstatehouse.gov |accessdate=2015-03-01}}</ref> and [[Arkansas]]<ref>{{cite web|url=http://www.arkleg.state.ar.us/assembly/2005/R/Pages/BillInformation.aspx?measureno=HB1770 |title=Bill Information |publisher=Arkleg.state.ar.us |date= |accessdate=2015-01-28}}</ref> use "instant runoff" to describe the practice of having certain categories of absentee voters cast ranked choice ballots before the first round of a runoff and counting those ballots in any subsequent runoff elections. |
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=== Resistance to strategy === |
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When the [[single transferable vote]] (STV) system is applied to a single-winner election it becomes IRV. Some Irish observers mistakenly call IRV "proportional representation" based on the fact that the same ballot form is used to elect its president by IRV and parliamentary seats by STV, but IRV is a winner-take-all election method. |
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Instant-runoff voting has notably high resistance to [[Strategic voting|tactical voting]] but less to [[strategic nomination]]. |
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==== Party strategizing and strategic nomination ==== |
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==History== |
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In Australia, preference deals (where one party's voters agree to place another party's voters second, in return for their doing the same) between parties are common. Parties and candidates often encourage their supporters to participate in these preference deals using [[How-to-vote card|How-to-vote cards]] explaining how to use their lower rankings to maximize the chances of their ballot helping to elect someone in the preference deal before it may exhaust.<ref>{{cite web |date=20 May 2022 |title=Explained: What are 'preference deals' and how do they influence my vote? |url=https://www.9news.com.au/national/explainer-preference-deals-and-how-australias-voting-system-works/7078d92b-d6a6-4b37-919a-3aad0a13e873 |website=[[Nine News|9News]]}}</ref> |
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{{Main|History and use of instant-runoff voting}} |
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Instant runoff may be manipulable via strategic candidate entry and exit, reducing similar candidates' chances of winning. Such manipulation does not need to be intentional, instead acting to deter candidates from running in the first place.<ref name="d138">{{cite journal | last=Robinette | first=Robbie | title=Implications of strategic position choices by candidates | journal=Constitutional Political Economy | publisher=Springer Science and Business Media LLC | volume=34 | issue=3 | date=2023-02-02 | issn=1043-4062 | doi=10.1007/s10602-022-09378-6 | doi-access=free | pages=445–457}}</ref> Spatial model simulations indicate that instant runoff rewards strategic withdrawal by candidates.<ref name="Armytage 2014">{{cite journal | first=James|last=Green-Armytage | title=Strategic voting and nomination | journal=Social Choice and Welfare | publisher=Springer | volume=42 | issue=1 | year=2014 | issn=0176-1714 | jstor=43663746 | pages=111–138 | doi=10.1007/s00355-013-0725-3 | s2cid=253847024 | url=http://www.jstor.org/stable/43663746 | access-date=2024-02-23}}</ref>{{efn| name="ExitIncentive"|Figure 4 on page 137 shows instant-runoff voting having exit incentive despite being clone independent.}} |
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Instant-runoff voting was devised in 1871 by American [[architect]] [[William Robert Ware]],<ref>{{cite web|author=Benjamin Reilly |url=http://archive.fairvote.org/articles/reilly.pdf |title= |
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The Global Spread of Preferential Voting: Australian Institutional Imperialism |publisher=FairVote.org |accessdate=17 April 2011}}</ref> although it is, in effect, a special case of the [[single transferable vote]] system, which emerged independently in the 1850s. Unlike the single transferable vote in multi-seat elections, however, the only ballot transfers are from backers of candidates who have been eliminated. |
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==== Tactical voting ==== |
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The first known use of an IRV-like system in a governmental election was in 1893 in an election for the [[self-governing colony|colonial]] government of [[Queensland]], in Australia.<ref>{{cite web|url=http://www.nuffield.ox.ac.uk/Politics/papers/2002/w23/mclean.pdf|format=PDF|title=Australian electoral reform and two concepts of representation|author=McLean, Iain|date=October 2002|accessdate=22 February 2008|page=11}}</ref> The variant used for this election was a "contingent vote". IRV in its true form was first used in 1908 in a State election in [[Western Australia]]. |
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{{See also|Tactical voting#Instant runoff voting}} |
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[[Gibbard's theorem]] demonstrates that no (deterministic, non-dictatorial) voting method can be entirely immune from tactical voting. This implies that IRV is susceptible to tactical voting in some circumstances. In particular, when there exists a [[Condorcet winner]] who IRV fails to elect, voters who prefer the Condorcet winner to the IRV winner have an incentive to use the [[Tactical voting#Types of strategic voting|compromising]] strategy.<ref name="Armytage 2014" />{{rp|at=proposition 17}} IRV is also sometimes vulnerable to a paradoxical strategy of ranking a candidate higher to make them lose, due to IRV failing the [[monotonicity criterion]].<ref>{{cite web |title=Monotonicity and IRV – Why the Monotonicity Criterion is of Little Import |url=http://archive.fairvote.org/?page=2261 |access-date=17 April 2011 |website=archive.fairvote.org}}</ref> |
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Research suggests that IRV is very resistant to tactical voting. In a test of multiple methods, instant runoff was found to be the second-most-resistant to tactical voting, after a class of instant runoff-[[Condorcet method|Condorcet]] hybrids.<ref name=":0">{{Cite journal |journal=[[Voting matters]] |title=Four Condorcet-Hare Hybrid Methods for Single-Winner Elections |url=https://www.votingmatters.org.uk/ISSUE29/I29P1.pdf |year=2011 |access-date=2024-10-25|first=James|last=Green-Armytage}}</ref> IRV is also completely immune to the ''burying'' strategy: ranking a strong opposition candidate lower can't get one's preferred candidate elected.<ref name="Armytage 2014" />{{rp|at=proposition 3}} |
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IRV was introduced nationally in Australia in 1918 after the [[Swan by-election, 1918|Swan by-election]], in response to the rise of the conservative [[National Party of Australia|Country Party]], representing small farmers. The Country Party split the anti-Labor vote in conservative country areas, allowing Labor candidates to win on a minority vote. The conservative government of [[Billy Hughes]] introduced preferential voting as a means of allowing competition between the two conservative parties without putting seats at risk. It was first used at the [[Division of Corangamite|Corangamite]] by-election on 14 December 1918.<ref>{{cite web|url=http://australianpolitics.com/elections/features/voting-methods-history.shtml |title=Australian Electoral History: Voting Methods |publisher=Australianpolitics.com |accessdate=17 April 2011}}</ref> [[Thomas Hare (political scientist)|Thomas Hare]] and [[Andrew Inglis Clark]] had previously introduced it in the [[Tasmanian House of Assembly]]. |
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Tactical voting in IRV seeks to alter the order of eliminations in early rounds, to ensure that the original winner is challenged by a stronger opponent in the final round. For example, in a three-party election where voters for both the [[Left-wing politics|left]] and [[Right-wing politics|right]] prefer the [[Centrism|centrist]] candidate to stop the opposing candidate from winning, those voters who care more about defeating the opposition than electing their own candidate may cast a tactical first-preference vote for the centrist candidate. |
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==Election procedure== |
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=== |
==== Spoiler effect ==== |
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{{main|Spoiler effect}} |
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[[File:IRV counting flowchart.svg|300px|right|thumb|Flowchart for counting IRV votes]] |
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Proponents of IRV claim that IRV eliminates the spoiler effect, since IRV makes it safe to vote honestly for marginal parties. Under a plurality method, voters who sympathize most strongly with a marginal candidate are strongly encouraged to instead vote for a more popular candidate who shares some of the same principles, since that candidate has a much greater chance of being elected and a vote for the marginal candidate will not result in the marginal candidate's election. An IRV method reduces this problem, since the voter can rank the marginal candidate first and the mainstream candidate second; in the likely event that the fringe candidate is eliminated, the vote is not wasted but is transferred to the second preference. |
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However, when the third-party candidate is more competitive, they can still act as a spoiler under IRV,<ref name=":043">{{Cite book |last=Borgers |first=Christoph |url=https://books.google.com/books?id=u_XMHD4shnQC |title=Mathematics of Social Choice: Voting, Compensation, and Division |publisher=SIAM |year=2010 |isbn=9780898716955 |quote=Candidates C and D spoiled the election for B ... With them in the running, A won, whereas without them in the running, B would have won. ... Instant runoff voting ... does ''not'' do away with the spoiler problem entirely, although it ... makes it less likely}}</ref><ref name=":723">{{Cite book |last=Poundstone |first=William |url=https://books.google.com/books?id=_24bJHyBV6sC |title=Gaming the Vote: Why Elections Aren't Fair (and What We Can Do About It) |publisher=Farrar, Straus and Giroux |year=2009 |isbn=9781429957649 |quote=IRV is excellent for preventing classic spoilers-minor candidates who irrationally tip the election from one major candidate to another. It is not so good when the 'spoiler' has a real chance of winning}}</ref><ref name="Burlington23">{{cite journal |author=Bristow-Johnson, R. |year=2023 |title=The failure of Instant Runoff to accomplish the purpose for which it was adopted: a case study from Burlington Vermont |url=https://doi.org/10.1007/s10602-023-09393-1 |format=PDF |journal=Const Polit Econ |volume=34 |issue=3 |pages=378–389 |doi=10.1007/s10602-023-09393-1 |s2cid=255657135 |access-date=9 January 2024}}</ref> by taking away first-choice votes from the more mainstream candidate until that candidate is eliminated, and then that candidate's second-choice votes helping a more-disliked candidate to win. In these scenarios, it would have been better for the third party voters if their candidate had not run at all (spoiler effect), or if they had voted dishonestly, ranking their favourite second rather than first (favorite betrayal).<ref>{{Cite SSRN |last=O'Neill |first=Jeffrey C. |date=2006 |title=Everything That Can be Counted Does Not Necessarily Count: The Right to Vote and the Choice of a Voting System |page=340 |ssrn=883058 |quote=With instant runoff voting ... The strategy for the liberal voter is the same as for plurality voting: Her favorite candidate cannot win, so she casts her vote for her favorite candidate with a realistic chance of winning}}</ref>{{Better source needed|reason=The current source is insufficiently reliable ([[WP:NOTRS]]).|date=September 2024}} This is the same bracketing effect exploited by Robinette and Tideman in their research on strategic campaigning, where a candidate alters their campaign to cause a change in voter honest choice, resulting in the elimination of a candidate who nevertheless remains more preferred by voters. |
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[[File:Hor ballot paper.gif|Australian Preferential ballot]] |
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For example, in the [[2009 Burlington mayoral election|2009 Burlington, Vermont, mayoral election]], if the Republican candidate who lost in the final instant runoff had not run, the Democratic candidate would have defeated the winning Progressive candidate. In that sense, the Republican candidate was a spoiler—albeit for an opposing Democrat, rather than some political ally—even though leading in first choice support.<ref name="Burlington23" /> This also occurred in the [[2022 Alaska's at-large congressional district special election]]. If Republican [[Sarah Palin]], who lost in the final instant runoff, had not run, the more centrist Republican candidate, Nick Begich, would have defeated the winning Democratic candidate, [[Mary Peltola]].<ref>{{cite arXiv |eprint=2209.04764v1 |class=econ.GN |first1=Adam |last1=Graham-Squire |first2=David |last2=McCune |title=A Mathematical Analysis of the 2022 Alaska Special Election for US House |date=2022}}</ref> |
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In instant-runoff voting, as with other ranked election methods, each voter ranks the list of candidates in order of preference. Under a common [[Ranked voting systems#Ballot variations|ballot]] layout, the voter marks a '1' beside the most preferred candidate, a '2' beside the second-most preferred, and so forth, in [[ascending order]]. This is shown in the example Australian ballot above. |
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== Reception == |
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The mechanics of the process are the same regardless of how many candidates the voter ranks, and how many are left unranked. In some implementations, the voter ranks as many or as few choices as they wish, while in other implementations the voter is ''required'' to rank either all candidates, or a prescribed number of them. |
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The system has had a mixed reception among [[Political science|political scientists]] and [[Social choice theory|social choice theorists]].<ref name=":3">{{cite news |last1=Drutman |first1=Lee |last2=Strano |first2=Maresa |date=10 November 2021 |title=What We Know About Ranked-Choice Voting |url=https://www.newamerica.org/political-reform/reports/what-we-know-about-ranked-choice-voting/conclusion/ |access-date=28 February 2023 |publisher=New America}}</ref><ref name="auto2">{{Cite web |last=Drutman |first=Lee |date=2023-09-18 |title=How I updated my views on ranked choice voting |url=https://leedrutman.substack.com/p/how-i-updated-my-views-on-ranked |access-date=2024-09-02 |website=Undercurrent Events}}</ref> Some have suggested that the system does not do much to decrease the impact of [[Wasted vote|wasted votes]] relative to plurality.<ref name=":23">{{Cite web |date=10 April 2017 |title=Understanding the Limited Preferential Voting system – EMTV Online |url=https://emtv.com.pg/understanding-the-limited-preferential-voting-system/ |access-date=18 February 2021}}</ref><ref name=":433" /><ref name=":035">{{Cite journal |last1=Endersby |first1=James W. |last2=Towle |first2=Michael J. |date=2014-03-01 |title=Making wasted votes count: Turnout, transfers, and preferential voting in practice |url=https://www.sciencedirect.com/science/article/abs/pii/S0261379413000930 |journal=Electoral Studies |volume=33 |pages=144–152 |doi=10.1016/j.electstud.2013.07.001 |issn=0261-3794}}</ref> Research has found IRV causes lower confidence in elections<ref name="auto1">{{Cite web |title=The Effect of Ranked-Choice Voting in Maine {{!}} MIT Election Lab |url=https://electionlab.mit.edu/articles/effect-ranked-choice-voting-maine |access-date=2024-09-02 |website=electionlab.mit.edu}}</ref><ref name=":06">{{Cite journal |last1=Cerrone |first1=Joseph |last2=McClintock |first2=Cynthia |date=August 2023 |title=Come-from-behind victories under ranked-choice voting and runoff: The impact on voter satisfaction |url=https://onlinelibrary.wiley.com/doi/10.1111/polp.12544 |journal=Politics & Policy |language=en |volume=51 |issue=4 |pages=569–587 |doi=10.1111/polp.12544 |issn=1555-5623}}</ref><ref name="auto3">{{Cite journal |last=Nielson |first=Lindsay |date=August 2017 |title=Ranked Choice Voting and Attitudes toward Democracy in the United States: Results from a Survey Experiment |url=https://onlinelibrary.wiley.com/doi/10.1111/polp.12212 |journal=Politics & Policy |language=en |volume=45 |issue=4 |pages=535–570 |doi=10.1111/polp.12212 |issn=1555-5623}}</ref> and does not substantially affect minority representation,<ref name=":623">{{Cite web |title=The Short-Term Impact of Ranked-Choice Voting on Candidate Entry and Descriptive Representation |url=https://www.newamerica.org/political-reform/reports/rcv-impact-on-candidate-entry-and-representation/ |access-date=2024-09-02 |website=New America |language=en}}</ref> [[voter turnout]],<ref name=":3" /><ref name=":035" /> or long-run [[electoral competition]].<ref name=":3" /><ref name=":623" /> Opponents have also noted a high rate of repeals for the system.<ref name=":06"/> |
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=== Voter confusion and legitimacy === |
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[[File:Hand marking ranked ballot.JPG|thumb| left|[[Optical scan voting system|Optical scan]] IRV ballot]] |
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Governor [[Paul LePage]]<ref>{{cite web |last=Leary |first=Mal |date=12 June 2018 |title=Opposed To Ranked-Choice Voting, LePage Says He Might Not Certify Primary Election Results |url=http://www.mainepublic.org/post/opposed-ranked-choice-voting-lepage-says-he-might-not-certify-primary-election-results |access-date=14 January 2019 |website=Maine Public}}</ref> and Representative Bruce Poliquin<ref>{{Cite Pacer|plaintiff=Baber|defendant=Dunlap|title=Complaint|doc-number=1|date=13 November 2018|recap-number=8169811|case-state=ME|case-division=1|case-year=18|case-type=cv|case-sequence=00465|access-date=13 January 2019}}</ref> claimed, ahead of the 2018 primary elections, that IRV would result in "one person, five votes", as opposed to "[[one person, one vote]]". Federal judge Lance Walker rejected these claims, and the 1st circuit court denied Poliquin's emergency appeal.<ref>{{cite news |date=22 December 2018 |title=1st Circuit ends Poliquin's efforts to keep House seat |url=https://bangordailynews.com/2018/12/21/politics/1st-circuit-ends-poliquins-efforts-to-keep-house-seat/ |access-date=17 August 2019 |website=Bangor Daily News}}</ref> |
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=== Similarity to plurality === |
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In the initial count, the first preference of each voter is counted and used to order the candidates. Each first preference counts as one vote for the appropriate candidate. Once all the first preferences are counted, if one candidate holds a [[majority]], that candidate wins. Otherwise the candidate who holds the fewest first preferences is eliminated. If there is an exact tie for last place in numbers of votes, [[#Handling ties|tie-breaking rules]]{{dead link|date=June 2015}} determine which candidate to eliminate. Some jurisdictions eliminate all low-ranking candidates simultaneously whose combined number of votes is fewer than the number of votes received by the lowest remaining candidates. |
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Often instant-runoff voting elections are won by the candidate who leads in first-count vote tallies so they choose the same winner as [[first-past-the-post voting]] would have. In Australia federal elections, the [[1972 Australian federal election|1972 election]] had the largest number of winners who would not have won under first past the post but still only 14 out of 125 seats filled were not won by the first-count leader.<ref>{{Cite web |last=Green |first=Antony |date=11 May 2010 |title=Preferential Voting in Australia |url=https://www.abc.net.au/news/2010-05-12/preferential-voting-in-australia/9389472 |access-date=1 November 2020 |website=www.abc.net.au}}</ref> |
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=== Participation === |
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Ballots assigned to eliminated candidates are recounted and assigned to one of the remaining candidates based on the next preference on each ballot. The process repeats until one candidate achieves a majority of votes cast for continuing candidates. Ballots that |
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'exhaust' all their preferences (all its ranked candidates are eliminated) are set aside. |
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The effect of IRV on voter turnout is difficult to assess. In a 2021 report, researchers at [[New America (organization)|New America]], a [[think tank]] based in Washington, D. C., said it may increase turnout by attracting more and more diverse candidates, but the impact would be realized most significantly by getting rid of the need for primaries.<ref name="auto12">{{Cite web |title=What We Know About Ranked-Choice Voting |url=http://newamerica.org/political-reform/reports/what-we-know-about-ranked-choice-voting/ |website=New America}}</ref> The overall impact on diversity of candidates is difficult to detect.<ref name=":3"/> |
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In Australian elections the allocation of preferences is performed efficiently at the polling booth by having the [[returning officer]] pre-declare the two likely winners. (In the event that the returning officer is wrong the votes need to be recounted.) |
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==Terminology== |
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While instant run-off voting is distinguished from its multiple winner equivalent, the [[single transferable vote]], in most English-speaking discussion of electoral systems, no distinction between the two is made in [[Republic of Ireland|Ireland]], one of the few countries to use these systems in all elections, either by the general population or in legal texts. The [[Constitution of Ireland]] describes the electoral system as "proportional representation by means of the single transferable vote"<ref>ref name="Articles 16.2.5°, 12.2.3°, and 18.5, Constitution of Ireland">{{cite web |date=January 2020 |title=Constitution of Ireland (English) |url=https://www.irishstatutebook.ie/eli/cons/en/html |access-date=19 December 2024 |publisher=Office of the Attourney General}}</ref>, as do all other statutory authorities, when referring to either single-winner or multiple-winner elections. The acronym "PR-STV" is in general use to describe both types of elections. Examples of single-winner elections in Ireland which are described officially as "proportional representation by means of the single transferable vote" are the [[Irish presidential election|election of the President]] and the [[2024 Ceann Comhairle election|election of the Ceann Comhairle]] (chairperson of [[Dáil Éireann]]). The lack of distinction between the systems in Ireland reflects that there is no difference in the mechanics of the process from election to election, only the number of candidates to be elected by that process. This is not always the case when discussing the systems in the abstract, as there are many variations in how such elections could be run. |
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As seen above, voters in an IRV election rank candidates on a [[Ranked voting systems|preferential ballot]]. IRV systems in use in different countries vary both as to ballot design and as to whether or not voters are obliged to provide a full list of preferences. In elections such as those for the President of Ireland and the [[New South Wales Legislative Assembly]], voters are permitted to rank as many (or as few) candidates as they wish. This is known in Australia as '''optional preferential voting'''. |
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Instant-runoff voting derives its name from the way the ballot count simulates a series of runoffs, similar to an [[Exhaustive ballot|exhaustive ballot system]], except that voters do not need to turn out several times to vote.<ref name="publications.parliament.uk2">{{cite web |date=15 February 2001 |title=Second Report: Election of a Speaker |url=https://publications.parliament.uk/pa/cm200001/cmselect/cmproced/40/4005.htm |access-date=18 February 2008 |publisher=House of Commons Select Committee on Procedure}}<!--This ref describes similarities/differences between IRV and exhaustive ballot.--></ref> It is also known as the alternative vote, transferable vote, ranked-choice voting (RCV), single-seat ranked-choice voting, or preferential voting (but use of some of those terms may lead to misunderstanding as they also apply to STV.)<ref>{{Cite journal |last=Cary |first=David |date=1 January 2011 |title=Estimating the Margin of Victory for Instant-runoff Voting |url=http://dl.acm.org/citation.cfm?id=2028012.2028015 |journal=Proceedings of the 2011 Conference on Electronic Voting Technology/Workshop on Trustworthy Elections |series=EVT/WOTE'11 |pages=3}}</ref> |
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Under optional preferential voting, voters may make only a first choice, known as "[[bullet voting]]". Allowing voters to rank only as many candidates as they wish may better reflect their preferences, but may result in [[#Ballot exhaustion|ballot exhaustion]] (where all the voters' preferences are eliminated before a candidate is elected). |
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Britons and New Zealanders generally call IRV the "alternative vote" (AV).<ref>{{cite web |date=8 February 2012 |title=BBC News – Alternative vote |url=https://www.bbc.com/news/uk-politics-12910547 |access-date=9 October 2019 |website=bbc.com |publisher=British Broadcasting Corporation}}</ref><ref>{{cite web |date=30 September 2017 |title=Opinion: OUSA Needs the Alternative Vote |url=https://www.critic.co.nz/news/article/7194/opinion-ousa-needs-the-alternative-vote |access-date=9 October 2019 |website=Critic – Te Arohi |publisher=Otago University Students' Association |location=Otago, New Zealand}}</ref> Australians, who use IRV for most single winner elections, call IRV "preferential voting".<ref>{{cite news |date=11 December 2020 |title=Liberal plan to change federal voting laws may have crossbench support |url=https://www.theguardian.com/australia-news/2020/dec/12/liberal-plan-to-change-federal-voting-laws-may-have-crossbench-support |access-date=13 February 2021 |work=The Guardian}}</ref> While this term is widely used by Australians, it is somewhat of a [[misnomer]]. Depending on how "preferential" is defined, the term would include all voting systems, apply to any system that uses ranked ballots (thus both IRV and STV), or would exclude IRV (IRV fails [[Monotonicity criterion|positive responsiveness]] because ballot markings are not interpreted as "preferences" in the traditional sense. Under IRV (and STV), secondary preferences are used as back-up preferences/contingency votes). |
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One IRV variant requires voters to express an order of preference for every candidate and thus they consider ballots that do not contain a complete ordering of all candidates to be [[spoilt vote|spoilt]]. In Australia, this variant is known as 'full preferential voting'.<ref>{{cite web|url=http://www.eca.gov.au/systems/single/by_category/preferential.htm|title=Electoral Systems|publisher=Electoral Council of Australia|accessdate=15 February 2008}}</ref> This can become burdensome in elections with many candidates and can lead to '[[donkey voting]]' in which the voter simply chooses candidates at random or in top-to-bottom order. [This variant is used in [[Australian electoral system|some Australian federal elections]] and [[Electoral systems of the Australian states and territories|some state elections]]]. |
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Jurisdictions in the United States such as [[San Francisco]], [[Minneapolis]], [[Maine]], and [[Alaska]] have tended to use the term "ranked-choice voting" in their laws that apply to IRV contests. The San Francisco Department of Elections claimed the word "instant" in the term "instant-runoff voting" could confuse voters into expecting results to be immediately available.<ref>Appendix D, Instant Runoff Voting, San Francisco Charter § 13.102 https://sfgov.org/ccsfgsa/sites/default/files/Voting%20Systems%20Task%20Force/AppendixD__.pdf.</ref><ref>{{cite web |last=Arntz |first=John |date=2 February 2005 |title=Ranked-Choice Voting: A Guide for Candidates |url=http://www.fairvote.org/media/irv/sanfrancisco/RCVCandidateGuide04.pdf |archive-url=https://web.archive.org/web/20081202040611/http://fairvote.org/media/irv/sanfrancisco/RCVCandidateGuide04.pdf |archive-date=2 December 2008 |access-date=25 August 2009 |publisher=Department of Elections: City and County of San Francisco |via=[[FairVote]] |quote=In San Francisco, ranked-choice voting is sometimes called 'instant run-off voting.' The Department of Elections generally uses the term ranked-choice voting, because it describes the voting method—voters are directed to rank their first-, second- and third-choice candidates. The Department also uses the term ranked-choice voting because the word 'instant' might create an expectation that final results will be available immediately after the polls close on election night.}}</ref> As a result of American influence, the term ranked-choice voting is often used in Canada as well.<ref name="auto">{{cite web |title=What is Ranked Choice Voting? |url=http://www.london.ca/city-hall/elections/ranked-choice-voting/Pages/What-is-Ranked-Choice-Voting.aspx |archive-url=https://web.archive.org/web/20180226101409/http://www.london.ca/city-hall/elections/ranked-choice-voting/Pages/What-is-Ranked-Choice-Voting.aspx |archive-date=26 February 2018 |website=City of London}}</ref> American NGO [[FairVote]] has promoted the terminology "ranked-choice voting" to refer to IRV,<ref name="auto" /><ref>{{cite web |date=17 August 2019 |title=How RCV Works |url=https://www.fairvote.org/rcv#how_rcv_works |access-date=17 August 2018 |website=FairVote}}</ref> a choice that has caused controversy and accusations that the organization is attempting to obscure the existence of other [[Ranked voting|ranked-choice]] methods that could compete with IRV.{{Cn|date=May 2024}} |
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===Candidate order on the ballot paper=== |
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The common way to list candidates on a ballot paper is alphabetically or by random lot. In some cases, candidates may also be grouped by political party. Alternatively, [[Robson Rotation]] involves randomly changing candidate order for each print run. |
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IRV is occasionally referred to as Hare's method<ref>{{Cite encyclopedia |title=Voting Methods |encyclopedia=The Stanford Encyclopedia of Philosophy |url=https://plato.stanford.edu/archives/fall2019/entries/voting-methods/ |last=Pacuit |first=Eric |date=24 June 2019 |orig-date=3 August 2011 |editor1-last=Zalta |editor1-first=Edward N. |edition=Fall 2019 |via=plato.stanford.edu}}</ref> (after [[Thomas Hare (political scientist)|Thomas Hare]]) to differentiate it from other ranked-choice voting methods such as [[Condorcet winner criterion|majority-choice voting]], [[Borda count|Borda]], and [[Bucklin voting|Bucklin]], which use weighted preferences or methods that allow voter's lower preference to be used against voter's most-preferred choice. |
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===Party strategies=== |
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Where preferential voting is used for the election of an assembly or council, parties and candidates often advise their supporters on their lower preferences, especially in Australia where a voter must rank all candidates to cast a valid ballot. This can lead to "preference deals", a form of pre-election bargaining, in which smaller parties agree to direct their voters in return for support from the winning party on issues critical to the small party.{{citation needed|date=November 2010}} However, this relies on the assumption that supporters of a minor party will mark preferences for another party based on the advice that they have been given. |
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When the [[single transferable vote]] (STV) method is applied to a single-winner election, it becomes IRV; the government of Ireland has called IRV "proportional representation" based on the fact that the same ballot form is used to elect its president by IRV and parliamentary seats by proportional representation (STV), but IRV is a non-proportional winner-take-all (single-winner) election method, while STV elects multiple winners.<ref>{{cite web |title=Proportional Representation |url=https://www.citizensinformation.ie/en/government_in_ireland/elections_and_referenda/voting/proportional_representation.html |access-date=17 August 2019 |publisher=Citizens Information Board}}</ref> |
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===Counting logistics=== |
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Most IRV elections historically have been tallied by hand, including in elections to [[Australia]]'s House of Representatives and most state governments. In the modern era, voting equipment can be used to administer the count either partially or fully. |
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State law in [[South Carolina]]<ref>{{cite web |title=South Carolina General Assembly : 116th Session, 2005–2006 |url=http://www.scstatehouse.gov/sess116_2005-2006/bills/3720.doc |access-date=1 March 2015 |website=Scstatehouse.gov}}</ref> and [[Arkansas]]<ref>{{cite web |title=Bill Information |url=http://www.arkleg.state.ar.us/assembly/2005/R/Pages/BillInformation.aspx?measureno=HB1770 |access-date=28 January 2015 |website=Arkleg.state.ar.us}}</ref> use "instant runoff" to describe the practice of having certain categories of absentee voters cast ranked-choice ballots before the first round of an election and counting those ballots in any subsequent runoff elections. |
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In Australia, the returning officer now usually declares the two candidates that are most likely to win each seat. The votes are always counted by hand at the polling booth monitored by scrutineers from each candidate. The first part of the count is to record the first choice for all candidates. Votes for candidates other than the two likely winners are then allocated to them in a second pass. The whole process of counting the votes by hand and allocating preferences is typically completed within two hours on election night at a cost of $7.68 per elector in 2010 to run the entire election.<ref name="aec.gov.au">[http://www.aec.gov.au/about_aec/publications/electoral_pocketbook/2011/ep-costs.htm Australian Electoral Commission.]</ref> |
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==History and use== |
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(The declaration by the returning officer is simply to optimize the counting process. In the unlikely event that the returning officer is wrong and a third candidate wins, then the votes would simply have to be counted a third time.)<ref>{{cite web|url=http://blogs.abc.net.au/antonygreen/2011/02/how-the-alternative-vote-works.html |title=Antony Green's Election Blog: How the Alternative Vote Works |publisher=Blogs.abc.net.au |date=2011-02-20 |accessdate=2014-04-30}}</ref> |
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{{Main|History and use of instant-runoff voting}} |
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=== History === |
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Ireland in its presidential elections has several dozen counting centers around the nation. Each center reports its totals and receives instructions from the central office about which candidate or candidates to eliminate in the next round of counting based on which candidate is in last place. The count typically is completed the day after the election, as in 1997.<ref>{{cite web|url=http://archive.fairvote.org/sf/SFLawsuit_Richie.pdf |format=PDF |title=Declaration of Robert Richie in Support of Petition for Writ of Mandate |publisher=Archive.fairvote.org |accessdate=2015-03-01}}</ref> |
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This method was first discussed by the [[Marquis de Condorcet]] in 1788, who quickly rejected it after showing it would often eliminate a candidate preferred by a majority of voters.<ref name=":032"/><ref>{{Cite book |last=Condorcet |first=Jean-Antoine-Nicolas de Caritat |chapter-url=https://books.google.com/books?id=d0cwAAAAYAAJ&q=Oeuvres%20de%20Condorcet,%20Volume%2013&pg=PA243 |chapter=On the Constitution and the Functions of Provincial Assemblies |date=1788 |title=Complete Works of Condorcet |volume=13 |publication-date=1804 |pages=243 |language=fr |quote=En effet, lorsqu'il y a plus de trois concurrents, le véritable vœu de la pluralité peut être pour un candidat qui n'ait eu aucune des voix dans le premier scrutin.}}</ref> |
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IRV was later independently reinvented by [[Thomas Hare (political reformer)|Thomas Hare]] (of England) and Carl Andrae (of Denmark) in the form of the [[single transferable vote]]. [[Henry Richmond Droop]] then proposed applying the system to single-winner contests. (He also invented the [[Droop quota]], which equates to a simple majority in a single-winner contest.) |
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In the United States, some Californian cities, e.g. [[Oakland]] and [[San Francisco]], administer IRV elections on voting machines, with optical scanning machines recording preferences and software tallying the IRV algorithm.<ref>{{cite web|author=Wellfire Interactive |url=http://www.fairvote.org/reforms/instant-runoff-voting/irv-resources/ranked-voting-and-election-integrity-2/ |title=Ranked Voting and Election Integrity |publisher=FairVote.org |date=2008-06-25 |accessdate=2014-04-30}}</ref> [[Cary, North Carolina]]'s pilot program in 2007 tallied first choices on optical scan equipment at the polls and then used a central hand-count for the IRV tally.<ref>{{cite web|url=http://archive.fairvote.org/?page=2543 |title=FairVote - Wake County Answers on IRV Election Administration |publisher=Archive.fairvote.org |accessdate=2014-04-30}}</ref> [[Portland, Maine]] in 2011 was due to use its usual voting machines to tally first choice at the polls, then a central scan with different equipment if an IRV tally was necessary.<ref>{{cite web|url=http://www.mpbn.net/Home/tabid/36/ctl/ViewItem/mid/3478/ItemId/17382/Default.aspx |title=Maine Public Broadcasting Network, Maine News & Programming |publisher=Mpbn.net |accessdate=2014-04-30}}</ref> |
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=== Global use === |
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{{main|History and use of instant-runoff voting#Use by country}} |
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Some examples of IRV elections are given below. The first two (fictional elections) demonstrate the principle of IRV. The others offer examples of the results of real elections. |
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==== National level elections ==== |
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A simple example is provided in the accompanying table. Three candidates are running for election, Bob, Bill and Sue. There are five voters, "a" through "e". The voters each have one vote. They rank the candidates first, second and third in the order they prefer them. To win, a candidate must have a majority of vote; that is, three or more. |
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In Round 1, the first-choice rankings are tallied, with the results that Bob and Sue both have two votes and Bill has one. No candidate has a majority, so a second "instant runoff" round is required. Since Bill is in bottom place, he is eliminated. The ballot ranking him first is added to the totals of the candidate listed second. This results in the Round 2 votes as seen below. This gives Sue 3 votes, which is a majority. |
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{| class="wikitable" |
{| class="wikitable" |
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! width=150| Country |
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! width=150| Body or office |
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! width=180| Type of body or office |
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! scope="col" | [[Electoral system]] |
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! scope="col" | Total seats |
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! scope="col" | Notes |
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|- |
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! scope="row" | Australia |
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!| |
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|[[Australian House of Representatives|House of Representatives]] |
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! colspan="6" | Round 1 |
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|Lower chamber of legislature |
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! colspan="6" | Round 2 |
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|IRV |
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|151 |
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| |
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|- |
|- |
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! rowspan="2" scope="row" | Ireland |
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| '''Candidate''' || a || b || c || d || e |
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|[[President of Ireland|President]] |
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|| Votes || a || b || c || d || e || Votes |
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|Head of State |
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|- |
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|IRV |
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|| Bob||1||2||3||1||2|| style="background:#dfb;"|2||1||2||2||1||2||style="background:#fbb;"|''2'' |
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| |
| |
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| |
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|| Sue||3||1||2||3||1|| style="background:#dfb;"|2||2||1||1||2||1||style="background:#bfb;"|'''3''' |
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|- |
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|| Bill||2||3||1||2||3|| style="background:#fbb;"|''1'' |
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|} |
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===Tennessee capital election=== |
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Most instant-runoff voting elections are won by the candidate who leads in first-choice rankings.{{cn|date=August 2015}} In such cases, IRV chooses the same winner as [[first-past-the-post voting]]. Some IRV elections are won by a candidate who finishes second after the first-round count. In this case, IRV chooses the same winner as a [[two-round system]] if all voters were to vote again and maintain their same preferences. A candidate may also win who is in third place or lower after the first count, but gains majority support in the final round. In such cases, IRV would choose the same winner as a multi-round system that eliminated the last-place candidate before each new vote, assuming all voters kept voting and maintained their same preferences. Here is an example of this last case. |
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{{Tenn_voting example}} |
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In the first round no city gets a majority: |
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{| class="wikitable" |
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|- |
|- |
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|[[Dáil Éireann]] |
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!Votes in round/<br />City Choice !! 1st |
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|Lower chamber of legislature |
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|[[Single transferable vote]] (STV), by-elections using IRV |
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|158<ref name="fn_22">The [[Ceann Comhairle]] or Speaker of [[Dáil Éireann]] is returned automatically for whichever constituency s/he was elected if they wish to seek re-election, reducing the number of seats contested in that constituency by one. (In that case, should the Ceann Comhairle be from a three-seater, only two seats are contested in the general election from there.) As a result, if the Ceann Comhairle wishes to be in the next Dáil, only 165 seats are actually contested in a general election.</ref> |
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| |
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|- |
|- |
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! scope="row" | Papua New Guinea |
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| Memphis || style="background:#dfb;"|42% |
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|[[National Parliament of Papua New Guinea|National Parliament]] |
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|Unicameral legislature |
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|IRV |
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|109 |
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| |
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|- |
|- |
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! rowspan="3" scope="row" | United States |
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|Nashville || style="background:#dfb;"|26% |
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|[[President of the United States|President]] (via [[United States Electoral College|Electoral College]]) |
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|Head of State and Government |
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|[[Alaska]] and [[Maine]] use IRV to select the state's electoral college seat winner or winners. In Maine, 2 electors are allocated to the winner of the state vote plurality and the others (currently 2) are allocated by plurality in each congressional district. In Alaska, the winner gets all Electoral College electors of the state (as Alaska has only one ''at-large'' district, the effect is the same). |
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|7 EVs<ref>electoral votes</ref> (out of 538) |
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| |
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|- |
|- |
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|[[United States House of Representatives|House of Representatives]] |
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|Knoxville || style="background:#dfb;"|17% |
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|Lower chamber of legislature |
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| rowspan="2" |IRV in Maine |
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Nonpartisan primary system with IRV in the second round (among top four candidates) in Alaska.<ref name="boston.com2">{{cite web |date=10 November 2016 |title=Maine became the first state in the country Tuesday to pass ranked-choice voting |url=https://www.boston.com/news/politics/2016/11/10/maine-became-the-first-state-in-the-country-to-pass-ranked-choice-voting |access-date=10 November 2016}}</ref><ref>{{cite web |title=Ranked Choice Voting {{!}} Maine Voters Rank Candidates |url=http://mainerankedchoice.vote/ |access-date=8 April 2018 |website=Maine Uses Ranked Choice Voting |archive-date=4 April 2018 |archive-url=https://web.archive.org/web/20180404201657/http://mainerankedchoice.vote/ |url-status=dead }}</ref><ref name="Maine20182">{{cite news |last=Russell |first=Eric |date=12 June 2018 |title=Mainers vote to keep ranked-choice voting, with supporters holding commanding lead |url=https://www.pressherald.com/2018/06/12/ranked-choice-voting-takes-lead-in-early-balloting/ |access-date=13 June 2018 |work=Portland Press Herald}}</ref><ref>{{Cite web |title=Alaska Ballot Measure 2, Top-Four Ranked-Choice Voting and Campaign Finance Laws Initiative (2020) |url=https://ballotpedia.org/Alaska_Ballot_Measure_2,_Top-Four_Ranked-Choice_Voting_and_Campaign_Finance_Laws_Initiative_(2020) |access-date=17 November 2020 |website=Ballotpedia}}</ref> |
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|3 (out of 435) |
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| |
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|- |
|- |
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|[[United States Senate|Senate]] |
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|Chattanooga || style="background:#fbb;"|''15%'' |
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|Upper chamber of legislature |
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|4 (out of 100) |
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| |
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|} |
|} |
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=== ''Robert's Rules of Order'' === |
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If one of the cities had achieved a majority vote (more than half), the election would end there. If this were a first-past-the-post election, Memphis would win because it received the most votes. But IRV does not allow a candidate to win on the first round without having an absolute majority of the vote. While 42% of the electorate voted ''for'' Memphis, 58% of the electorate voted ''against'' Memphis in this first round. |
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In the United States, the sequential elimination method used by IRV is described in ''[[Robert's Rules of Order|Robert's Rules of Order Newly Revised]]'' as an example of [[Ranked voting systems|ranked-choice voting]] that can be used to elect officers.<ref name="autogenerated12">{{cite book |last=Robert |first=Henry |title=Robert's Rules of Order Newly Revised |publisher=Da Capo Press |year=2011 |isbn=978-0-306-82020-5 |edition=11th |pages=425–428}}</ref> ''Robert's Rules'' note that ranked-choice systems (including IRV) are an improvement on [[Plurality voting|simple plurality]] but recommend against runoff-based rules because they often prevent the emergence of a consensus candidate with broad support. The book instead recommends repeated balloting until some candidate manages to win a majority of votes. Two other books on American parliamentary procedure, ''[[The Standard Code of Parliamentary Procedure]]''<ref>{{cite parl|title=TSC|page=148|edition=4th}}</ref> and ''[[Riddick's Rules of Procedure]]'',<ref>{{cite parl|title=RID|page=145|edition=1985|year=1985}}</ref> take a similar stance. |
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==Similar methods== |
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So we move to the second round of tabulation to determine which of the front-running cities had broader support. Chattanooga received the lowest number of votes in the first round, so it is eliminated. The ballots that listed Chattanooga as “first-choice” are added to the totals of the second-choice selection on each ballot. Everything else stays the same. |
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===Runoff voting=== |
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{{Original research section|date=August 2024}} |
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The term ''instant-runoff voting'' is derived from the name of a class of voting methods called runoff voting. In runoff voting voters do not rank candidates in order of preference on a single ballot. Instead a similar effect is achieved by using multiple rounds of voting. All multi-round runoff voting methods allow voters to change their preferences in each round, incorporating the results of the prior round to influence their decision, which is not possible in IRV. |
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Chattanooga’s 15% of the total votes are added to the second choices selected by the voters for whom that city was first-choice (in this example Knoxville): |
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The runoff method closest to IRV is the [[exhaustive ballot]]. In this method—familiar to fans of the television show ''[[American Idol]]''—one candidate is eliminated after each round, and many rounds of voting are used, rather than just two. Because holding many rounds of voting on separate days is generally expensive, the exhaustive ballot is not used for large-scale, public elections. |
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{| class="wikitable" |
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|- |
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!Votes in round/<br />City Choice !! 1st !! 2nd |
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|- |
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| Memphis || style="background:#dfb;"|42% || style="background:#dfb;"|42% |
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|- |
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|Nashville || style="background:#dfb;"|26% || style="background:#fbb;"|''26%'' |
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|- |
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|Knoxville || style="background:#dfb;"|17% || style="background:#dfb;"|32% |
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|- |
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|Chattanooga || style="background:#fbb;"|''15%'' |
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|} |
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A more practical form of runoff voting is the [[two-round system]], which excludes all but the top-two candidates after the first round, rather than gradually eliminating candidates over a series of rounds. Eliminations can occur with or without allowing and applying preference votes to choose the final two candidates. A second round of voting or counting is only necessary if no candidate receives an overall majority of votes. This method is used in Mali, France and the Finnish and Slovenian presidential election. |
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In the first round, Memphis was first, Nashville was second and Knoxville was third. With Chattanooga eliminated and its votes redistributed, the second round finds Memphis still in first place, followed by Knoxville in second and Nashville has moved down to third place. No city yet has secured a majority of votes, so we move to the third round with the elimination of Nashville, and it becomes a contest between Memphis and Knoxville. |
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===Contingent vote=== |
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As in the second round with Chattanooga, all of the ballots currently counting for Nashville are added to the totals of Memphis or Knoxville based on which city is ranked next on that ballot. In this example the second-choice of the Nashville voters is Chattanooga, which is already eliminated. Therefore the votes are added to their third-choice: Knoxville. |
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{{Original research section|date=August 2024}} |
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[[File:IRV-toptwo_flowchart.png|thumb|Top-two IRV]] |
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The [[contingent vote]], also known as "top-two IRV", is the same as IRV, except that if no candidate achieves a majority in the first round of counting, all but the two candidates with the most votes are eliminated, and the second preferences for those ballots are counted. As in IRV, there is only one round of voting. |
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Under a variant of contingent voting used in [[Sri Lanka]], and formerly for the elections for [[Mayor of London]] in the United Kingdom, voters rank a specified maximum number of candidates. In London, the [[Contingent vote|supplementary vote]] allowed{{efn|Following the [[Elections Act 2022]], voting in mayoral elections now takes place under the [[First-past-the-post voting|first-past-the-post]] system.}} voters to express first and second preferences only. Sri Lankan voters [[Contingent vote#contingent vote in Sri Lanka|rank up to three candidates to elect the president of Sri Lanka]]. |
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The third round of tabulation yields the following result: |
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While similar to "sequential-elimination" IRV, top-two can produce different results. Excluding more than one candidate after the first count might eliminate a candidate who would have won under sequential elimination IRV. Restricting voters to a maximum number of preferences is more likely to exhaust ballots if voters do not anticipate which candidates will finish in the top two. This can encourage voters to vote more [[Tactical voting|tactically]], by ranking at least one candidate they think is likely to win. |
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{| class="wikitable" |
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|- |
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!Votes in round/<br />City Choice !! 1st !! 2nd !! 3rd |
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|- |
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| Memphis || style="background:#dfb;"|42% || style="background:#dfb;"|42% || style="background:#fbb;"|''42%'' |
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|- |
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|Nashville || style="background:#dfb;"|26% || style="background:#fbb;"|''26%'' |
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|- |
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|Knoxville || style="background:#dfb;"|17% || style="background:#dfb;"|32% || style="background:#bfb;"|'''58%''' |
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|- |
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|Chattanooga || style="background:#fbb;"|''15%'' |
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|} |
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Conversely, a practical benefit of 'contingent voting' is expediency and confidence in the result with only two rounds. |
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'''Result:''' Knoxville, which was running third in the first tabulation, has moved up from behind to take first place in the third and final round. The winner of the election is '''Knoxville'''. However, if 6% of voters in Memphis were to put Nashville first, the winner would be Nashville, a preferable outcome for voters in Memphis. This is an example of potential tactical voting, though one that would be difficult for voters to carry out in practice. Also, if 17% of voters in Memphis were to stay away from voting, the winner would be Nashville. This is an example of IRV failing the participation criterion. |
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===Larger runoff process=== |
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For comparison, note that traditional [[first-past-the-post voting]] would elect Memphis, even though most citizens consider it the worst choice, because 42% is larger than any other single city. As Nashville is a Condorcet winner, [[Condorcet method#Example: Voting on the location of Tennessee's capital|Condorcet methods]] would elect Nashville. A [[two-round system#Example II|two-round system]] would have a runoff between Memphis and Nashville where Nashville would win, too. |
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IRV may also be part of a larger runoff process: |
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* Some jurisdictions that hold runoff elections allow absentee (only) voters to submit IRV ballots, because the interval between votes is too short for a second round of absentee voting. IRV ballots enable absentee votes to count in the second (general) election round if their first choice does not make the runoff. [[Arkansas]], [[South Carolina]] and [[Springfield, Illinois]] adopt this approach.<ref>{{cite web |title=Initiatives – Pew Center on the States |url=http://www.electionline.org/Portals/1/Publications/SC.EAP.2006primary.pdf |archive-url=https://web.archive.org/web/20080516235221/http://www.electionline.org/Portals/1/Publications/SC.EAP.2006primary.pdf |archive-date=16 May 2008 |access-date=6 May 2010 |website=Electionline.org}}</ref> Louisiana uses it only for members of the United States Service or who reside overseas.<ref>{{Citation |title=IRV for Louisiana's Overseas Voters |type=web page |url=http://archive.fairvote.org/?page=1669 |access-date=16 June 2013 |publisher=FairVote IRV America}}</ref>{{Better source needed|reason=The current source is insufficiently reliable ([[WP:NOTRS]]).|date=September 2024}}{{Update needed|date=September 2024}} |
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===2006 Burlington mayoral election=== |
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* IRV can quickly eliminate weak candidates in early rounds of an [[exhaustive ballot]] runoff, using rules to leave the desired number of candidates for further balloting. |
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{{See also|Instant-runoff voting in the United States#2006 Burlington results}} |
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* IRV elections that require a majority of cast ballots but not that voters rank all candidates may require more than a single IRV ballot due to exhausted ballots. |
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{| class="wikitable" style="text-align:center; float:right; margin-left:1em" |
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* Robert's Rules recommends [[Ranked voting systems|preferential voting]] for elections by mail and requiring a majority of cast votes to elect a winner. For in-person elections, they recommend repeated balloting until one candidate receives an absolute majority of all votes cast; if candidates drop out as soon as it becomes clear they cannot win, this procedure will always elect a [[Condorcet method|Condorcet winner]]. The use of repeated balloting allows voters to resolve [[Condorcet paradox|Condorcet cycles]] by discussion and compromise, or by electing a consensus candidate who might have polled poorly in the initial election.<ref name="autogenerated12" /> |
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|- |
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!Candidate |
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!colspan=2|Round 1 |
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!colspan=2|Round 2 |
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|- |
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![[Bob Kiss]] |
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| 3,809 || ''(38.9%)'' |
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| 4,761 || ''(48.6%)'' |
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|- |
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![[Hinda Miller]] |
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| 3,106||''(31.7%)'' |
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| 3,986||''(40.7%)'' |
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|- |
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!Kevin Curley |
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| 2,609||''(26.7%)'' |
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|colspan=2 | — |
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|- |
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!Other |
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|254||''(2.6%)'' |
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|colspan=2 | — |
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|- |
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!Exhausted ballots |
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|10||''(0.1%)'' |
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|1,041||''(10.5%)'' |
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|- |
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!Total |
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|9,778||''(100%)'' |
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|9,778||''(100%)'' |
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|} |
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In 2006, the U.S. city of [[Burlington, Vermont]], held a mayoral election using instant-runoff voting. Progressive [[Bob Kiss]] won in two rounds with 48.6% of the second round ballots, defeating Democrat [[Hinda Miller]] who achieved 40.7%. 10.6% (1,031) of the ballots were exhausted before the final round, because those voters (largely backers of Republican candidate Kevin Curley) offered no preference between the final two candidates, Miller and Kiss.<ref>{{cite web|url= http://www.burlingtonvotes.org/20060307/2006%20Burlington%20Mayor%20Round3.htm|title= 2006 Burlington mayoral election|date= 7 March 2006|publisher= Voting Solutions |accessdate= 22 February 2008}}</ref> |
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After the first round, all but two candidates were eliminated, as their combined vote total (2,863) was less than Miller's, so that none could pull ahead of Miller, even by receiving every vote from the other minor candidates. The votes for these candidates were recounted and redistributed between Kiss and Miller. After the second round count, Kiss was declared the winner as he had obtained a majority (54.4%) of the remaining unexhausted ballots. |
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{{-}} |
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===1990 Irish presidential election=== |
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{{See also|Irish presidential election, 1990}} |
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{|class="wikitable" style="float:right; text-align:center; margin:10px" |
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|- |
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! colspan=5|Irish presidential election, 1990<ref> |
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{{cite web |
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|url=http://www.electionsireland.org/result.cfm?election=1990P&cons=194 |
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|title=Presidential Election November 1990 |
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|work=ElectionsIreland.org |
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|accessdate=23 November 2009 |
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}}</ref> |
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|- |
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!Candidate |
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!colspan=2|Round 1 |
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!colspan=2|Round 2 |
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|- |
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![[Mary Robinson]] |
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|612,265 || ''(38.9%)'' |
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|817,830 || ''(51.6%)'' |
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|- |
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![[Brian Lenihan, Snr|Brian Lenihan]] |
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|694,484||''(43.8%)'' |
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|731,273||''(46.2%)'' |
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|- |
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![[Austin Currie]] |
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|267,902||''(16.9%)'' |
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|colspan=2 | — |
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|- |
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!Exhausted ballots |
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|9,444||''(0.6%)'' |
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|34,992||''(2.2%)'' |
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|- |
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!Total |
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|1,584,095||''(100%)'' |
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|1,584,095||''(100%)'' |
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|} |
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The result of the [[Irish presidential election, 1990|1990 Irish presidential election]] provides an example of how instant-runoff voting can produce a different result than [[first-past-the-post voting]]. The three candidates were [[Brian Lenihan, Snr|Brian Lenihan]] of the traditionally dominant [[Fianna Fáil]] party, [[Austin Currie]] of [[Fine Gael]], and [[Mary Robinson]], nominated by the [[Labour Party (Ireland)|Labour Party]] and the [[Workers' Party of Ireland|Worker's Party]]. After the first round, Lenihan had the largest share of the first-choice rankings (and hence would have won a first-past-the-post vote), but no candidate attained the necessary majority. Currie was eliminated and his votes reassigned to the next choice ranked on each ballot; in this process, Robinson received 82% of Currie's votes, thereby overtaking Lenihan.<!-- no cite: since only 3 candidates just simple ratio of extra votes in 2nd count. --> |
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{{clr}} |
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==Voting system criteria== |
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Scholars rate voting systems using mathematically derived [[voting system criterion|voting system criteria]], which describe desirable features of a system. No ranked preference method can meet all of the criteria, because some of them are mutually exclusive, as shown by statements such as [[Arrow's impossibility theorem]] and the [[Gibbard-Satterthwaite theorem]]. |
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Many of the mathematical criteria by which voting systems are compared were formulated for voters with ordinal preferences. If voters vote according to the same ordinal preferences in both rounds, criteria can be applied to [[two-round system]]s of runoffs, and in that case, each of the criteria failed by IRV is also failed by the [[two-round system]] as they relate to automatic elimination of trailing candidates. Partial results exist for other models of voter behavior in the two-round system: see the [[Two-round system#Compliance with voting system criteria|two-round system article's criterion compliance section]] for more information. |
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The criteria that IRV meets, and those that it does not, are listed below. |
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===Majority criterion=== |
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{{Tick}} The '''[[majority criterion|majority]]''' criterion states that "if one candidate is preferred by an absolute majority of voters, then that candidate must win". IRV meets this criterion. |
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===Mutual majority criterion=== |
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{{Tick}} The '''[[mutual majority criterion|mutual majority]]''' criterion states that "if an absolute majority of voters prefer every member of a group of candidates to every candidate not in that group, then one of the preferred group must win". IRV meets this criterion. |
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===Later-no-harm criterion=== |
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{{Tick}} The '''[[later-no-harm criterion|later-no-harm]]''' criterion states that "if a voter alters the order of candidates lower in his/her preference (e.g. swapping the second and third preferences), then that does not affect the chances of the most preferred candidate being elected". IRV meets this criterion. |
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===Resolvability criterion=== |
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{{Tick}} The '''[[resolvability criterion|resolvability]]''' criterion states that "the probability of an exact tie must diminish as more votes are cast". IRV meets this criterion. |
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===Condorcet winner criterion=== |
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{{Cross}} The '''[[Condorcet criterion|Condorcet winner]]''' criterion states that "if a candidate would win a [[Condorcet method|head-to-head competition]] against every other candidate, then that candidate must win the overall election". It is incompatible with the later-no-harm criterion, so IRV does not meet this criterion. |
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IRV is more likely to elect the Condorcet winner than plurality voting and traditional runoff elections. The California cities of Oakland, San Francisco and San Leandro in 2010 provide an example; there were a total of four elections in which the plurality voting leader in first choice rankings was defeated, and in each case the IRV winner was the Condorcet winner, including a San Francisco election in which the IRV winner was in third place in first choice rankings.<ref>{{cite web|author=FairVote |url=http://www.fairvote.org/understanding-the-rcv-election-results-d10 |title=Understanding the RCV Election Results in District 10 |publisher=FairVote.org |accessdate=17 April 2011}}</ref> |
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===Condorcet loser criterion=== |
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{{Tick}} The '''[[Condorcet loser criterion|Condorcet loser]]''' criterion states that "if a candidate would lose a [[Condorcet method|head-to-head competition]] against every other candidate, then that candidate must not win the overall election". IRV meets this criterion. |
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===Consistency criterion=== |
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{{Cross}} The '''[[consistency criterion|consistency]]''' criterion states that if dividing the electorate into two groups and running the same election separately with each group returns the same result for both groups, then the election over the whole electorate should return this result. IRV, like all preferential voting systems which are not [[positional voting system|positional]], does not meet this criterion. |
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===Monotonicity criterion=== |
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{{Further|Monotonicity criterion#Instant-runoff voting and the Two-round system are not monotonic}} |
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{{Cross}} The '''[[monotonicity criterion|monotonicity]]''' criterion states that "a voter can't harm a candidate's chances of winning by voting that candidate higher, or help a candidate by voting that candidate lower, while keeping the relative order of all the other candidates equal." IRV does not meet this criterion. Allard<ref>{{cite web|author=Crispin Allard|url=http://www.mcdougall.org.uk/VM/ISSUE5/P1.HTM|title=Estimating the Probability of Monotonicity Failure in a UK General Election|date=January 1996|accessdate=4 May 2011}}</ref> claims failure is unlikely, at a less than 0.03% chance per election. Some critics<ref>{{cite web|author=Warren D. Smith|url=http://rangevoting.org/Monotone.html|title=Monotonicity and Instant Runoff Voting|accessdate=4 May 2011}}</ref> argue in turn that Allard's calculations are wrong and the probability of monotonicity failure is much greater, at 14.5% under the impartial culture election model in the three-candidate case, or 7-10% in the case of a left-right spectrum. Lepelly ''et al.''<ref>Dominique Lepelley, Frederic Chantreuil, Sven Berg: [http://www.sciencedirect.com/science/article/B6V88-3VW8PC1-1/2/5abd6699c83d02dcfe329cdee91aec22 The likelihood of monotonicity paradoxes in run-off elections], Mathematical Social Sciences 31 (1996) 133-146</ref> find a 2%-5% probability of monotonicity failure under the same election model as Allard. |
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===Participation criterion=== |
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{{Cross}} The '''[[participation criterion|participation]]''' criterion states that "the best way to help a candidate win must not be to abstain".<ref>More precisely, submitting a ballot that ranks A ahead of B should never change the winner from A to B.</ref> IRV does not meet this criterion: in some cases, the voter's preferred candidate can be best helped if the voter does not vote at all.<ref name="WDSParticipationReversalSymmetry">{{cite web|author=Warren D. Smith|url=http://rangevoting.org/TBlecture.html#partic|title=Lecture "Mathematics and Democracy"|accessdate=12 May 2011}}</ref> Depankar Ray<ref>{{cite web|author=Depankar Ray|url=http://www.sciencedirect.com/science/article/B6V88-46RVD34-6/2/4ade9a3bc999c9d9f295fea853253435|title=On the practical possibility of a "no show paradox" under the single transferable vote, Mathematical Social Sciences 11,2 (1986) 183-189|accessdate=14 May 2011}}</ref> finds a 50% probability that, when IRV elects a different candidate than Plurality, some voters would have been better off not showing up. |
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===Reversal symmetry criterion=== |
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{{Cross}} The '''[[reversal symmetry]]''' criterion states that "if candidate A is the unique winner, and each voter's individual preferences are inverted, then A must not be elected". IRV does not meet this criterion: it is possible to construct an election where reversing the order of every ballot paper does not alter the final winner.<ref name="WDSParticipationReversalSymmetry"/> |
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===Independence of irrelevant alternatives criterion=== |
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{{Cross}} The '''[[independence of irrelevant alternatives]]''' criterion states that "the election outcome remains the same even if a candidate who cannot win decides to run." IRV does not meet this criterion; in the general case, instant-runoff voting can be susceptible to [[strategic nomination]]: whether or not a candidate decides to run at all can affect the result even if the new candidate cannot themselves win.<ref name="wds">{{cite web|url=http://rangevoting.org/Burlington.html |title=Burlington Vermont 2009 IRV mayoral election |publisher=RangeVoting.org |accessdate=17 April 2011}}</ref> This is much less likely to happen than under plurality.{{citation needed|date=January 2015}} |
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===Independence of clones criterion=== |
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{{Tick}} The '''[[independence of clones criterion]]''' states that "the election outcome remains the same even if an identical candidate who is equally preferred decides to run." IRV meets this criterion.<ref>Green-Armytage, James (2004) [http://www.econ.ucsb.edu/~armytage/voting/survey.htm A Survey of Basic Voting Methods]</ref> |
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==Comparison to other voting systems== |
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===Comparison of mechanics=== |
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Instant-runoff voting is one of many ranked ballot systems. For example, the elimination of the candidate with the most last-place rankings, rather than the one with the fewest first-place rankings, is called [[Coombs' method]], and universal assignment of numerical values to each rank is used in the [[Borda count]] method. A chart in the article on the [[Schulze method#Comparison table|Schulze method]] compares various ranked ballot systems. |
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===Comparison to first-past-the-post=== |
===Comparison to first-past-the-post=== |
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In the [[2013 Australian federal election|Australian federal election in September 2013]], 135 out of the 150 [[Australian House of Representatives|House of Representatives]] seats (or 90 percent) were won by the candidate who led on first preferences. The other 15 seats (10 percent) were won by the candidate who placed second on first preferences.<ref>[[Antony Green]] (8 September 2015). [http://blogs.abc.net.au/antonygreen/2015/09/preferences-donkey-votes-and-the-canning-by-election.html Preferences, Donkey Votes and the Canning By-Election] – Antony Green's Election Blog (Australian Broadcasting Corporation). Retrieved 8 September 2015.</ref>{{Better source needed|reason=The current source is insufficiently reliable ([[WP:NOTRS]]).|date=September 2024}} |
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=== Variations === |
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==Resistance to tactical voting== |
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[[File:2016-ballot-paper-Higgins.png|thumb|Example of a full preferential ballot paper from the [[Australian House of Representatives]]]] |
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A number of IRV methods, varying as to ballot design and as to whether or not voters are obliged to provide a full list of preferences, are in use in different countries and local governments. |
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In an [[optional preferential voting]] system, voters can give a preference to as many candidates as they wish. They may make only a single choice, known as "[[bullet voting]]", and some jurisdictions accept a single box marked with an "X" (as opposed to a numeral "1") as valid for the first preference. This may result in exhausted ballots, where all of a voter's preferences are eliminated before a candidate is elected, such that the "majority" in the final round may only constitute a minority fraction of all ballots cast. Optional preferential voting is used for elections for the [[President of Ireland]] as well as some elections in [[New South Wales]] and [[Queensland]].<ref>{{cite web |date=28 January 2020 |title=Voting system |url=https://www.ecq.qld.gov.au/how-to-vote/voting-systems |access-date=17 November 2020 |website=www.ecq.qld.gov.au |publisher=Electoral Commission of Queensland}}</ref><ref>{{cite web |last1=Stevens |first1=Bronwyn |date=27 January 2015 |title=Are Queenslanders in danger of 'wasting' their votes? |url=https://www.theconversation.com/amp/are-queenslanders-in-danger-of-wasting-their-votes-35919 |access-date=28 November 2020 |website=The Conversation}}</ref> |
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The [[Gibbard–Satterthwaite theorem]] demonstrates that no voting system using only the preference rankings of the voters can be entirely immune from tactical voting unless it is dictatorial (there is only one person who is able to choose the winner) or incorporates an element of chance. This implies that IRV is susceptible to tactical voting in some circumstances. |
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In a full-preferential voting method, voters are required to mark a preference for every candidate standing.<ref>{{cite web |title=Electoral Systems |url=http://www.eca.gov.au/systems/single/by_category/preferential.htm |archive-url=https://web.archive.org/web/20080309220219/http://www.eca.gov.au/systems/single/by_category/preferential.htm |archive-date=9 March 2008 |access-date=15 February 2008 |publisher=Electoral Council of Australia}}</ref> Ballots that do not contain a complete ordering of all candidates are in some jurisdictions considered [[Spoilt vote|spoilt]] or invalid, even if there are only two candidates standing. This can become burdensome in elections with many candidates and can lead to "[[donkey voting]]", in which some voters simply choose candidates at random or in top-to-bottom order, or a voter may order his or her preferred candidates and then fill in the remainder on a donkey basis. Full preferential voting is used for elections to the [[Australian electoral system|Australian federal parliament]] and for most [[Electoral systems of the Australian states and territories|state parliaments]]. |
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Nonetheless, IRV is considered one of the less-manipulable voting systems, with theorist [[Nicolaus Tideman]] noting that, "alternative vote is quite resistant to strategy"<ref name=tac1>John J. Bartholdi III, [[James B. Orlin]] (1991) [http://www.isye.gatech.edu/~jjb/papers/stv.pdf "Single transferable vote resists strategic voting,"] ''Social Choice and Welfare,'' vol. 8, p. 341-354</ref> and Australian political analyst [[Antony Green]] dismissing suggestions of tactical voting.<ref>{{cite web|url=http://blogs.abc.net.au/antonygreen/2010/07/how-to-vote-guide.html|title=How to Vote Guide}}</ref> James Green-Armytage finds the alternative vote to be second most resistant to tactical voting among the methods tested, only beaten by a class of AV-Condorcet hybrids, although the alternative vote resists strategic withdrawal by candidates less well.<ref name=jga>{{cite web|url=http://www.econ.ucsb.edu/~armytage/hybrids.pdf|archiveurl=https://web.archive.org/web/20130603013310/http://www.econ.ucsb.edu/~armytage/hybrids.pdf|archivedate=3 June 2013|author=James Green-Armytage|title=Four Condorcet-Hare Hybrid Methods for Single-Winner Elections|accessdate=31 May 2011}}</ref> |
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Other methods only allow marking preferences for a maximum of the voter's top three favourites, a form of partial preferential voting.<ref>{{cite web |title=Ranked-Choice Voting |url=http://www.acgov.org/rov/rcv/faq.htm |access-date=15 December 2016 |website=Registrar of Voters, Alameda County |quote=This format allows a voter to select a first-choice candidate in the first column, a second-choice candidate in the second column, and a third-choice candidate in the third column.}}</ref> |
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By not meeting the monotonicity, Condorcet winner, and participation criteria, IRV permits forms of tactical voting when voters have sufficient information about other voters' preferences, such as from accurate pre-election polling.<ref name=tac3 /> [[FairVote]] mentions that monotonicity failure can lead to situations where "Having more voters rank [a] candidate first, can cause [them] to switch from being a winner to being a loser."<ref>{{cite web|url=http://archive.fairvote.org/?page=2261 |title=Monotonicity and IRV - Why the Monotonicity Criterion is of Little Import |publisher=Archive.fairvote.org |accessdate=17 April 2011}}</ref> That assessment is accurate, although it only happens in particular situations. The change in lower candidates is important: whether votes are shifted to the leading candidate, shifted to a fringe candidate, or discarded altogether is of no importance. |
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A version of instant-runoff voting applying to the ranking of parties was first proposed for elections in Germany in 2013<ref>{{cite report |title=Anhörung zum Entwurf eines Gesetzes zur Abschaffung der Fünf-Prozent-Sperrklausel bei Landtagswahlen in Schleswig-Holstein |trans-title=Hearing on the draft law to abolish the five percent threshold in state elections in Schleswig-Holstein (Discussion paper) |last1=Breyer |first1=Patrick |date=November 2013 |publisher=Piratenfraktion im Schleswig-Holsteinischen Landtag |language=de |id=(Drs. 18/385) |chapter=Alternative II: Einführung einer Ersatzstimme |chapter-url=https://www.landtag.ltsh.de/infothek/wahl18/umdrucke/1900/umdruck-18-1916.pdf}}</ref> as [[spare vote]].{{Citation needed|date=September 2024}} |
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Tactical voting in IRV seeks to alter the order of eliminations in early rounds, to ensure that the original winner is challenged by a stronger opponent in the final round. For example, in a three-party election where voters for both the left and right prefer the centrist candidate to stop the "enemy" candidate winning, those voters who care more about defeating the "enemy" than electing their own candidate may cast a tactical first preference vote for the centrist candidate. |
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== Voting method criteria == |
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The 2009 [[Burlington, Vermont mayoral election, 2009|mayoral election]] in [[Burlington, Vermont]] provides an example in which strategy theoretically could have worked but would have been unlikely in practice. In that election, most supporters of the candidate who came in second (a Republican who led in first choices) preferred the [[Condorcet method|Condorcet]] winner, a Democrat, to the IRV winner, the Progressive Party nominee. If about 20% of the backers of the Republican candidate had insincerely raised the Democrat from their second choice to their first, the Republican would have dropped from first to third in first choices, and the Democrat would then have won the instant runoff.<ref name=tac3>Warren Smith (2009) [http://rangevoting.org/Burlington.html "Burlington Vermont 2009 IRV mayor election; Thwarted-majority, non-monotonicity & other failures (oops)"]</ref> But given that the Republican was a strong candidate who nearly won in the instant runoff, few of his backers would have risked giving up on his candidacy based on a chance, unknown before the fact, to elect the compromise Condorcet winner. |
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{{main|Voting criteria}} |
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As shown by [[Arrow's impossibility theorem|Arrow]], [[Gibbard's theorem|Gibbard]], and others, it's usually impossible for a method to pass all of a number of seemingly reasonable properties, or criteria, at once. IRV is no exception: it passes some and fails others. The following criteria are satisfied and failed by IRV: |
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===Spoiler effect=== |
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{{main|Spoiler effect}} |
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=== Satisfied criteria === |
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The spoiler effect is where two or more politically similar candidates divide the vote for the more popular end of the political spectrum. That is, each receives fewer votes than a single opponent on the unpopular end of the spectrum who is disliked by the majority of voters but who wins from the advantage that, on that unpopular side, he or she is unopposed. |
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==== Condorcet loser Criterion ==== |
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Proponents of IRV note that by reducing the spoiler effect, IRV makes it safe to vote honestly for marginal parties, and so discourages [[tactical voting]]: under a plurality system, voters who sympathize most strongly with a marginal candidate are strongly encouraged to instead vote for a more popular candidate who shares some of the same principles, since that candidate has a much greater chance of being elected and a vote for the fringe candidate is largely wasted. |
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<blockquote>The [[Condorcet loser criterion|'''Condorcet loser''']] criterion states that "if a candidate would lose a [[Condorcet method|head-to-head competition]] against every other candidate, then that candidate must not win the overall election". IRV (like all voting methods with a final runoff round) meets this criterion, since the Condorcet loser cannot win a runoff. </blockquote> |
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==== Independence of clones criterion ==== |
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An IRV system reduces this problem, since the voter can rank the marginal candidate first and the mainstream candidate second; in the likely event that the fringe candidate is eliminated, the vote is not wasted but is transferred to the second preference. However, in the event that the fringe candidate is not eliminated immediately, there is an increased chance for the mainstream candidate to lose, especially when multiple fringe candidates are running. If that happens, the opposing mainstream candidate has a much easier path to victory. As a result, voting honestly for a fringe candidate is unlikely to benefit the voter, and may backfire. |
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<blockquote>The '''[[independence of clones criterion]]''' states that "the election outcome remains the same even if an identical candidate who is equally preferred decides to run". Advocates have noted that IRV meeting this criterion<ref>{{cite web |last1=Green-Armytage |first1=James |date=2004 |title=A Survey of Basic Voting Methods |url=http://www.econ.ucsb.edu/~armytage/voting/survey.htm |archive-url=https://web.archive.org/web/20130603015026/http://www.econ.ucsb.edu/~armytage/voting/survey.htm |archive-date=3 June 2013}}</ref><ref name="TC">{{cite journal | last=Tideman | first=T. N. | title=Independence of clones as a criterion for voting rules | journal=Social Choice and Welfare | publisher=Springer Science and Business Media LLC | volume=4 | issue=3 | year=1987 | issn=0176-1714 | doi=10.1007/bf00433944 | pages=185–206 | quote=Among previously proposed voting rules, the alternative vote and the GOCHA rule are independent of clones.}}</ref> greatly reduces the impact of clones compared to [[First-preference plurality|FPTP]]. </blockquote> |
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==== Later-no-harm criterion ==== |
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In Australia's national elections in 2007, the average number of candidates in a district was seven, and at least four candidates ran in every district; notwithstanding the fact that Australia only has two major political parties. Every seat was won with a majority of the vote, including several where results would have been different under plurality voting.<ref>{{cite web|url=http://results.aec.gov.au/13745/website/HouseResultsMenu-13745.htm |title=House of Representatives Results |publisher=Results.aec.gov.au |accessdate=2015-03-01}}</ref> While IRV reduces the severity of the spoiler effect compared to plurality voting, the problem still persists. |
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<blockquote>The [[Later-no-harm criterion|'''later-no-harm''']] criterion states that "if a voter alters the order of candidates lower in his/her preference (e.g. swapping the second and third preferences), then that does not affect the chances of the most preferred candidate being elected". Instant runoff satisfies this criterion. </blockquote> |
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==== Majority criterion ==== |
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==Proportionality== |
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<blockquote>The [[Majority favorite criterion|'''majority criterion''']] states that "if one candidate is preferred by an absolute majority of voters, then that candidate must win". Instant runoff also satisfies this criterion. </blockquote> |
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==== Mutual majority criterion ==== |
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IRV is not a proportional voting system. Like all winner-take-all voting systems, IRV tends to exaggerate the number of seats won by the largest parties; small parties without majority support in any given constituency are unlikely to earn seats in a legislature, although their supporters will be more likely to be part of the final choice between the two strongest candidates.<ref>{{cite web|url=http://www.mtholyoke.edu/acad/polit/damy/BeginnningReading/types.htm |title=Types of Voting Systems |publisher=Mtholyoke.edu |date=8 April 2005 |accessdate=6 May 2010}}</ref> A simulation of IRV in the [[United Kingdom general election, 2010|2010 UK general election]] by the [[Electoral Reform Society]] concluded that the election would have altered the balance of seats between the three main parties, but the number of seats won by minor parties would have remained unchanged.<ref>{{cite news|url=http://www.guardian.co.uk/politics/2010/may/10/alternative-vote-minimal-impact-general-election|accessdate=1 April 2011|date=10 May 2010|title=Electoral reform: Alternative vote system would have had minimal impact on outcome of general election|publisher=''[[The Guardian]]''|location=London|first=Alan|last=Travis}}</ref> |
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<blockquote>The [[Mutual majority criterion|'''mutual majority''']] criterion states that "if an absolute majority of voters prefer every member of a group of candidates to every candidate not in that group, then one of the preferred group must win". Note that this is satisfied because when all but one candidate that a mutual majority prefer is eliminated, the votes of the majority all flow to the remaining candidate, in contrast to [[FPTP]], where the majority would be treated as separate small groups. Instant runoff satisfies this criterion as well. </blockquote> |
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==== Resolvability criterion ==== |
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Australia, a nation with a long record of using IRV for the election of legislative bodies, has had representation in its parliament broadly similar to that expected by [[Plurality voting system|plurality systems]]. Medium-sized parties, such as the [[National Party of Australia]], can co-exist with [[Coalition (Australia)|coalition]] partners such as the [[Liberal Party of Australia]], and can compete against it without fear of losing seats to other parties due to vote splitting.<ref>[http://www.abc.net.au/elections/federal/2004/guide/prefhistory.htm History of Preferential Voting in Australia], [[Australian Broadcasting Corporation]], 2004 Election Guide. "''Such a long lasting Coalition would not have been possible under first part the post voting''"</ref> IRV is more likely to result in legislatures where no single party has an absolute majority of seats (a [[hung parliament]]),{{citation needed|date=May 2011}} but does not generally produce as fragmented a legislature as a fully proportional system, such as is used for the [[House of Representatives of the Netherlands]] or the [[New Zealand House of Representatives]], where coalitions of numerous small parties are needed for a majority. |
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<blockquote>The [[Resolvability criterion|'''resolvability''']] criterion states that "the probability of an exact tie must diminish as more votes are cast".{{Citation needed|date=September 2024}} </blockquote> |
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=== Failed criteria === |
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==Costs== |
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{{Original research section|date=September 2024}} |
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==== Condorcet winner criterion ==== |
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The costs of printing and counting ballot papers for an IRV election are no different from those of any other system using the same technology. However, the more-complicated counting system may encourage officials to introduce more advanced technology, such as software counters or electronic voting machines. [[Pierce County, Washington]] election officials outlined one-time costs of $857,000 to implement IRV for its elections in 2008, covering software and equipment, voter education and testing.<ref>{{cite web|url=http://www.ncvoter.net/downloads/Pierce_Co_WA_2008_IRV_Recap.pdf |title=Pierce County RCV Overview – City of LA Briefing |format=PDF |accessdate=6 May 2010}}</ref> In 2009, the auditor of Washington counties reported that the ongoing costs of the system were not necessarily balanced by the costs of eliminating runoffs for most county offices, because those elections may be needed for other offices not elected by IRV.<ref>{{cite web|url=https://blog.thenewstribune.com/politics/2009/05/06/pierce-county-auditor-sees-savings-from-scrapping-ranked-choice-voting/ |title=County auditor sees savings from scrapping ranked choice voting |publisher=Blogs.thenewstribune.com |date=30 August 2006 |accessdate=6 May 2010}}</ref> Other jurisdictions have reported immediate cost savings.<ref>{{cite web|url=http://archive.fairvote.org/?page=2543 |title=FairVote - Wake County Answers on IRV Election Administration |publisher=Archive.fairvote.org |accessdate=17 April 2011}}</ref> |
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The [[Condorcet criterion|'''Condorcet winner''']] criterion states that "if a candidate would win a [[Condorcet method|head-to-head competition]] against every other candidate, then that candidate must win the overall election". It is incompatible with the later-no-harm criterion, so IRV does not meet this criterion. |
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IRV is more likely to elect the Condorcet winner than [[plurality voting]] and [[Two-round system|traditional runoff]] elections. The California cities of Oakland, San Francisco and San Leandro in 2010 provide an example; there were a total of four elections in which the plurality-voting leader in first-choice rankings was defeated, and in each case the IRV winner was the Condorcet winner, including a San Francisco election in which the IRV winner was in third place in first choice rankings. |
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Australian elections are counted by hand. The 2010 federal election cost a total of $7.68 per elector of which only a small proportion is the actual counting of votes.<ref name="aec.gov.au"/> Counting is now normally performed in a single pass at the polling center as described above. |
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A particularly notable Condorcet failure occurred in the [[2009 Burlington mayoral election]]. |
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The perceived costs or cost savings of adopting an IRV system are commonly used by both supporters and critics. In the 2011 referendum on the Alternative Vote in the UK, the [[NOtoAV]] campaign was launched with a claim that adopting the system would cost £250 million; commentators argued that this headline figure had been inflated by including £82 million for the cost of the referendum itself, and a further £130 million on the assumption that the UK would need to introduce electronic voting systems, when ministers had confirmed that there was no intention of implementing such technology, whatever the outcome of the election.<ref>{{cite news|url=http://www.bbc.co.uk/news/uk-politics-12564879 |title=No to AV campaign reject rivals' 'scare stories' claim |publisher=Bbc.co.uk |date=24 February 2011 |accessdate=17 April 2011}}</ref> Automated vote counting is seen by some to have a greater potential for election fraud;<ref>{{cite web|url=http://www.ncvoter.net |title=Nc Voter |publisher=Nc Voter |accessdate=6 May 2010}}</ref> IRV supporters counter these claims with recommended audit procedures,<ref>{{cite web|url=http://www.fairvote.org/?page=2469 |title=Ranked Choice Voting and Election Integrity |publisher=FairVote |date=25 June 2008 |accessdate=6 May 2010}}</ref> or note that automated counting is not required for the system at all. |
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==== Independence of irrelevant alternatives ==== |
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Because it does not require two separate votes, IRV is accepted to cost less than [[two round system|two-round]] primary/general or general/runoff election systems.<ref>[http://sfpl4.sfpl.org/pdffiles/March5_2002.pdf] {{dead link|date=March 2015}}</ref> |
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The '''[[independence of irrelevant alternatives]]''' criterion states that "the election outcome remains the same even if a candidate who cannot win decides to run." Instant-runoff voting violates this. In the general case, instant-runoff voting can be susceptible to [[strategic nomination]]: whether or not a candidate decides to run at all can affect the result even if the new candidate cannot themselves win. This is less likely to happen than under plurality, but much more likely than under the [[Minimax Condorcet method]].<ref name="Armytage 2014" /> |
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==== Monotonicity criterion ==== |
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==Negative campaigning== |
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{{Further|Monotonicity criterion#Instant-runoff voting and the two-round system are not monotonic}} |
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The '''[[monotonicity criterion]]''' says that a voter ranking a candidate higher on their ballot should not cause that candidate to lose and conversely, that a voter ranking a candidate lower on their ballot should not help that candidate win. The exact probability of a monotonicity failure depends on the circumstances, but with 3 major candidates, the probabilities range from 15 percent under the [[impartial culture|impartial culture model]]<ref name="Miller">{{cite conference|title=Monotonicity failure in IRV elections with three candidates|last=Miller|first=Nicholas R.|year=2012|book-title=World meeting of the public choice societies}}</ref>{{rp|Table 6}} to 8.5 percent in the case of a strict [[Left–right political spectrum|left–right spectrum]].<ref>{{cite journal |last1=Lepelley |first1=Dominique |last2=Chantreuil |first2=Frederic |last3=Berg |first3=Sven |year=1996 |title=The likelihood of monotonicity paradoxes in run-off elections |journal=Mathematical Social Sciences |volume=31 |issue=3 |pages=133–146 |doi=10.1016/0165-4896(95)00804-7}}</ref> |
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==== Participation criterion ==== |
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John Russo, Oakland City Attorney, argued in the [[Oakland Tribune]] on 24 July 2006 that "Instant runoff voting is an antidote to the disease of negative campaigning. IRV led to San Francisco candidates campaigning more cooperatively. Under the system, their candidates were less likely to engage in negative campaigning because such tactics would risk alienating the voters who support 'attacked' candidates", reducing the chance that they would support the attacker as a second or third choice.<ref>{{cite news| url=http://www.nytimes.com/2004/09/30/national/30runoff.html | work=The New York Times | first=Dean E. | last=Murphy | title=New Runoff System in San Francisco Has the Rival Candidates Cooperating | date=30 September 2004}}</ref><ref>[http://findarticles.com/p/articles/mi_qn4176/is_20060724/ai_n16641454 Oakland Tribune, John Russo]{{Dead link|date=May 2010}}</ref> |
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The '''[[participation criterion]]''' says that candidates should not lose as a result of having "too many voters"—a set of ballots that all rank A>B should not switch the election winner from B to A. IRV fails this criterion. In his 1984 study, mathematician Depankar Ray found that in elections where IRV elects a different candidate from plurality, that there was an estimated 50 percent probability that some voters would have gotten a more preferable outcome if they had not participated.<ref name="auto4"/> |
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==== Reversal symmetry criterion ==== |
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No formal studies have been conducted in the United States. Internationally, Benjamin Reilly suggests instant-runoff voting eases ethnic conflict in divided societies.<ref>{{cite web|url=http://muse.jhu.edu/login?uri=/journals/journal_of_democracy/v013/13.2reilly.html |title=Project MUSE |publisher=Muse.jhu.edu |accessdate=6 May 2010}}</ref> This feature was a leading argument for why [[Papua New Guinea]] adopted instant-runoff voting.<ref>[http://aceproject.org/ero-en/regions/pacific/PG/Papua_new_guinea_leaflet.pdf/view "Papua New Guinea: Leaflet on Limited Preferential Voting System], Electoral Knowledg Network</ref> |
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The [[Reversal symmetry|reversal symmetry criterion]] states that the first- and last-place candidates should switch places if every ballot is reversed. In other words, it should not matter whether voters rank candidates from best-to-worst and select the best candidate, or whether they rank them worst-to-best and then select the least-bad candidate. |
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IRV fails this criterion: it is possible to construct an election where reversing the order of every ballot does not alter the final winner; that is, the first- and last-place finishers, according to IRV, are the same candidate.<ref>{{cite book |last=Felsenthal |first=Dan S. |title=Electoral Systems |chapter=Review of Paradoxes Afflicting Procedures for Electing a Single Candidate |date=2012 |series=Studies in Choice and Welfare |pages=19–91 [§ 3.5.2.4]|editor-last=Felsenthal |editor-first=Dan S. |chapter-url=http://link.springer.com/10.1007/978-3-642-20441-8_3 |access-date=2024-11-08 |location=Berlin, Heidelberg |publisher=Springer Berlin Heidelberg |doi=10.1007/978-3-642-20441-8_3 |isbn=978-3-642-20440-1 |editor2-last=Machover |editor2-first=Moshé}}</ref> |
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Critics allege there is a lack of evidence that such an effect occurs as often as suggested.<ref>{{cite web| url = http://www.beyondchron.org/news/index.php?itemid=1468 | title = Instant Runoff Voting Not Meeting Expectations | first = John | last = Dunbar | date = 17 November 2005}}</ref> Indeed, Lord Alexander's objections to the conclusions of the British Independent Commission on the Voting System's [http://www.archive.official-documents.co.uk/document/cm40/4090/chap-9.htm report] cites the example of Australia saying "their politicians tend to be, if anything, more blunt and outspoken than our own". |
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== |
=== Comparison to other voting systems === |
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{{Main article|Comparison of electoral systems}} |
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{{Comparison of Schulze to preferential voting systems}} |
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==Examples== |
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In [[Ann Arbor, Michigan]] arguments over IRV in letters to newspapers included the belief that IRV "gives minority candidate voters two votes", because some voters' ballots may count for their first choice in the first round and a lesser choice in a later round.<ref>{{cite web | url = http://www.migreens.org/hvgreens/aa-irv01.htm | title = History of Preferential Voting in Ann Arbor | first = Benjamin | last = Walter}}</ref> The argument that IRV represents [[plural voting]] is sometimes used in arguments over the 'fairness' of the system, and has led to several legal challenges in the United States. The argument was addressed and rejected by a Michigan court in 1975; in ''[[Stephenson v. the Ann Arbor Board of City Canvassers]]'', the court held "majority preferential voting" (as IRV was then known) to be in compliance with the Michigan and United States constitutions, writing:<ref>{{cite web|url=http://archive.fairvote.org/?page=397 |title=Ann Arbor Law Suit |publisher=FairVote |accessdate=10 May 2011}}</ref> |
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The first example is a fictional one for the purpose of demonstrating the principle of instant runoff. The other examples are drawn from the results of real-life elections. |
|||
{{quote|Under the 'M.P.V. System', however, no one person or voter has more than one effective vote for one office. No voter's vote can be counted more than once for the same candidate. In the final analysis, no voter is given greater weight in his or her vote over the vote of another voter, although to understand this does require a conceptual understanding of how the effect of a 'M.P.V. System' is like that of a run-off election. The form of majority preferential voting employed in the City of Ann Arbor's election of its Mayor does not violate the one-man, one-vote mandate nor does it deprive anyone of equal protection rights under the Michigan or United States Constitutions.|}} |
|||
=== Tennessee capital example === |
|||
==Invalid ballots and exhausted ballots== |
|||
{{Tenn_voting example}} |
|||
It takes three rounds to determine a winner in this election. |
|||
Because the ballot marking is more complex, there can be an increase in spoiled ballots. In Australia, voters are required to write a number beside every candidate, and error rates can be five times higher than plurality voting elections<ref>{{cite web|author=|url=http://www.no2av.org/why-vote-no/av-myth-busting/ |title=Busting the Myths of AV |publisher=No2av.org |date=25 October 2010 |accessdate=17 April 2011}}</ref> Since Australia has compulsory voting, however, it is difficult to tell how many ballots are deliberately spoiled.<ref>{{cite web|author=|url=http://blogs.abc.net.au/antonygreen/2011/02/informal-voting-two-ways-of-allowing-more-votes-to-count.html |title=Informal Voting - Two Ways of Allowing More Votes to Count |publisher=ABC Elections |date=28 February 2011 |accessdate=15 August 2011}}</ref> Most jurisdictions with IRV do not require complete rankings and may use columns to indicate preference instead of numbers. In American elections with IRV, more than 99% of voters typically cast a valid ballot.<ref>{{cite web|author=|url=http://politicalreform.newamerica.net/files/irvracememo.pdf |title=Instant Runoff Voting and Its Impact on Racial Minorities |publisher=New America Foundation |date=1 August 2008 |accessdate=15 August 2011}}</ref> |
|||
[[File:TN-round1.svg|right|frameless|175x175px]] |
|||
'''Round 1''' – In the first round no city gets a majority: |
|||
{| class="wikitable" |
|||
!Votes in round/ |
|||
City Choice |
|||
!1st |
|||
|- |
|||
|Memphis |
|||
| style="background:#dfb;" |42% |
|||
|- |
|||
|Nashville |
|||
| style="background:#dfb;" |26% |
|||
|- |
|||
|Knoxville |
|||
| style="background:#dfb;" |17% |
|||
|- |
|||
|Chattanooga |
|||
| style="background:#fbb;" |''15%'' |
|||
|} |
|||
If one of the cities had achieved a majority vote (more than half), the election would end there. If this were a first-past-the-post election, Memphis would win because it received the most votes. But IRV does not allow a candidate to win on the first round without having an absolute majority of the active votes. Since no city has won yet, the city with the least first-place support (Chattanooga) is eliminated from consideration. The ballots that listed Chattanooga as first choice are added to the totals of the second-choice selection on each ballot. |
|||
[[File:TN-round2.svg|right|frameless|161x161px]] |
|||
'''Round 2''' – In the second round of tabulation, Chattanooga's 15% of the total votes have been added to the second choices selected by the voters for whom that city was first-choice (in this example Knoxville): |
|||
{| class="wikitable" |
|||
!Votes in round/ |
|||
City Choice |
|||
!1st |
|||
!2nd |
|||
|- |
|||
|Memphis |
|||
| style="background:#dfb;" |42% |
|||
| style="background:#dfb;" |42% |
|||
|- |
|||
|Nashville |
|||
| style="background:#dfb;" |26% |
|||
| style="background:#fbb;" |''26%'' |
|||
|- |
|||
|Knoxville |
|||
| style="background:#dfb;" |17% |
|||
| style="background:#dfb;" |32% |
|||
|- |
|||
|Chattanooga |
|||
| style="background:#fbb;" |''15%'' |
|||
| |
|||
|} |
|||
In the first round, Memphis was first, Nashville was second and Knoxville was third. With Chattanooga eliminated and its votes redistributed, the second round finds Memphis still in first place, followed by Knoxville in second and Nashville has moved down to third place. No city yet has secured a majority of votes, so the now last placed Nashville is eliminated and the ballots currently counting for Nashville are added to the totals of Memphis or Knoxville based on which city is ranked next on that ballot. |
|||
'''Round 3''' |
|||
==Robert's Rules of Order== |
|||
[[File:TN-round3.svg|right|frameless|141x141px]] |
|||
As Memphis and Knoxville are the only two cities remaining in the contest, this round will be the final round. In this example the second-choice of the Nashville voters is Chattanooga, which is already eliminated. Therefore, the votes are added to their third-choice: Knoxville. The third round of tabulation yields the following result: |
|||
{| class="wikitable" |
|||
!Votes in round/ |
|||
City Choice |
|||
!1st |
|||
!2nd |
|||
!3rd |
|||
|- |
|||
|Memphis |
|||
| style="background:#dfb;" |42% |
|||
| style="background:#dfb;" |42% |
|||
| style="background:#fbb;" |''42%'' |
|||
|- |
|||
|Nashville |
|||
| style="background:#dfb;" |26% |
|||
| style="background:#fbb;" |''26%'' |
|||
|- |
|||
|Knoxville |
|||
| style="background:#dfb;" |17% |
|||
| style="background:#dfb;" |32% |
|||
| style="background:#bfb;" |'''58%''' |
|||
|- |
|||
|Chattanooga |
|||
| style="background:#fbb;" |''15%'' |
|||
|} |
|||
'''Result:''' Knoxville, which was running third in the first tabulation, has moved up from behind to take first place in the third and final round. The winner of the election is '''Knoxville'''. However, if 6% of voters in Memphis were to put Nashville first, the winner would be Nashville, a preferable outcome for voters in Memphis. This is an example of potential tactical voting, though one that would be difficult for voters to carry out in practice. Also, if 17% of voters in Memphis were to stay away from voting, the winner would be Nashville. This is an example of IRV failing the participation criterion. |
|||
For comparison, note that traditional [[first-past-the-post voting]] would elect Memphis, even though most citizens consider it the worst choice, because 42% is larger than any other single city. As Nashville is a Condorcet winner, [[Condorcet method#Example: Voting on the location of Tennessee's capital|Condorcet methods]] would elect Nashville. A [[Two-round system#Example II|two-round method]] would have a runoff between Memphis and Nashville where Nashville would win, too. |
|||
The sequential elimination method used by IRV is described in ''[[Robert's Rules of Order]] Newly Revised, 10th edition.''<ref name="autogenerated1"/> as an example of "[[Ranked voting systems|preferential voting]]", a term covering "any of a number of voting methods by which, on a single ballot when there are more than two possible choices, the second or less-preferred choices of voters can be taken into account if no candidate or proposition attains a majority. While it is more complicated than other methods of voting in common use, and is not a substitute for the normal procedure of repeated balloting until a majority is obtained, preferential voting is especially useful and fair in an election by mail if it is impractical to take more than one ballot. In such cases, it makes possible a more representative result than under a rule that a plurality shall elect...."Preferential voting has many variations. One method is described ... by way of illustration."<ref>{{harvnb|Robert|2000|p=411}}</ref> And then the instant runoff voting method is detailed.<ref>{{harvnb|Robert|2000|pp=412–413}}</ref> |
|||
===1990 Irish presidential election=== |
|||
''Robert's Rules'' continues: "The system of preferential voting just described should not be used in cases where it is possible to follow the normal procedure of repeated balloting until one candidate or proposition attains a majority. Although this type of preferential ballot is preferable to an election by plurality, it affords less freedom of choice than repeated balloting, because it denies voters the opportunity of basing their second or lesser choices on the results of earlier ballots, and because the candidate or proposition in last place is automatically eliminated and may thus be prevented from becoming a compromise choice."<ref name=roberts414>{{harvnb|Robert|2000|p=414}}</ref> Two other books on parliamentary procedure take a similar stance, disapproving of plurality voting and describing preferential voting as an option, if authorized in the bylaws, when repeated balloting is impractical: [[The Standard Code of Parliamentary Procedure]]<ref>{{cite parl|title=TSC|page=148|edition=4th}}</ref> and [[Riddick's Rules of Procedure]].<ref>{{cite parl|title=RID|page=145|edition=1985|year=1985}}</ref> |
|||
{{See also|Irish presidential election, 1990}} |
|||
The [[1990 Irish presidential election]] provides a simple example of how instant-runoff voting can produce a different result from [[first-past-the-post voting]] and prevent some spoiler effects associated with [[plurality voting]]. The three major candidates were [[Brian Lenihan Snr|Brian Lenihan]] of [[Fianna Fáil]], [[Austin Currie]] of [[Fine Gael]], and [[Mary Robinson]] of the [[Labour Party (Ireland)|Labour Party]]. After the first count, Lenihan had the largest share of first-choice rankings. Currie had the fewest votes and was eliminated. After this, Robinson received 82 percent of Currie's votes, thereby overtaking Lenihan. |
|||
{| class="wikitable" |
|||
|+Irish presidential election, 1990<ref>{{cite web |title=Presidential Election November 1990 |url=http://www.electionsireland.org/result.cfm?election=1990P&cons=194 |access-date=23 November 2009 |work=ElectionsIreland.org}}</ref> |
|||
!Candidate |
|||
! colspan="2" |Round 1 |
|||
! colspan="2" |Round 2 |
|||
|- |
|||
![[Mary Robinson]] |
|||
|612,265 |
|||
|38.9% |
|||
|'''817,830''' |
|||
|'''51.6%''' |
|||
|- |
|||
![[Brian Lenihan Snr|Brian Lenihan]] |
|||
|694,484 |
|||
|43.8% |
|||
|731,273 |
|||
|46.2% |
|||
|- |
|||
![[Austin Currie]] |
|||
|267,902 |
|||
|16.9%{{Xmark}} |
|||
| colspan="2" |''Eliminated'' |
|||
|- |
|||
!Exhausted ballots |
|||
|9,444 |
|||
|0.6% |
|||
|34,992 |
|||
|2.2% |
|||
|- |
|||
!Total |
|||
|1,584,095 |
|||
|100% |
|||
|1,584,095 |
|||
|100% |
|||
|} |
|||
<!--no cite: since only 3 candidates just simple ratio of extra votes in 2nd count.-->{{clear}} |
|||
===2014 Prahran election (Victoria)=== |
|||
==Global use== |
|||
Another real-life example of IRV producing results different from first-past-the-post can be seen in the [[2014 Victorian state election|2014 Victorian general election]] in [[Electoral district of Prahran|Prahran]]. In this rare instance, the candidate who initially placed third, ([[Australian Greens|Greens]] candidate [[Sam Hibbins]]), won the seat.<ref name="PrahranResults2">{{cite web |title=State Election 2014: Prahran District (Distribution of preference votes) |url=https://www.vec.vic.gov.au/Results/State2014/distributionPrahranDistrict.html |work=Victorian Electoral Commission |access-date=25 July 2018 |archive-date=25 July 2018 |archive-url=https://web.archive.org/web/20180725092627/https://www.vec.vic.gov.au/Results/State2014/distributionPrahranDistrict.html |url-status=dead }}</ref> In the 7th and final round, Hibbins narrowly defeated [[Liberal Party of Australia|Liberal]] candidate Clem Newton-Brown by a margin of 277 votes. |
|||
{{main|History and use of instant-runoff voting}} |
|||
{{see also|Table of voting systems by country}} |
|||
{| class="wikitable sortable" |
|||
===Australia=== |
|||
!Candidate |
|||
{{see also|Australian electoral system|Electoral systems of the Australian states and territories}} |
|||
! colspan="2" |1st |
|||
Instant-runoff voting is used for national elections in Australia to elect members of the [[Australian House of Representatives]]. The [[Australian Senate]] uses a modified form, combining it with a [[proportional representation]] system (the [[Single transferable vote]]); candidates are eliminated until the remaining parties can be said to have a sufficient proportion of the vote to earn a seat.<ref name="Australian Electoral Commission"/> Most state and council elections also use the system. |
|||
!2nd |
|||
!3rd |
|||
!4th |
|||
!5th |
|||
!6th |
|||
! colspan="2" |7th |
|||
|- |
|||
|[[Clem Newton-Brown]] ([[Liberal Party of Australia|LIB]]) |
|||
|44.8% |
|||
|'''16,582''' |
|||
|'''16,592''' |
|||
|'''16,644''' |
|||
|'''16,726''' |
|||
|'''16,843''' |
|||
|'''17,076''' |
|||
|18,363 |
|||
|49.6% |
|||
|- |
|||
|Neil Pharaoh ([[Australian Labor Party|ALP]]) |
|||
|25.9% |
|||
|'''9,586''' |
|||
|'''9,593''' |
|||
|'''9,639''' |
|||
|'''9,690''' |
|||
|'''9,758''' |
|||
|9,948{{Xmark}} |
|||
| colspan="2" |''Eliminated'' |
|||
|- |
|||
|[[Sam Hibbins]] ([[Australian Greens|GRN]]) |
|||
|24.8% |
|||
|9,160 |
|||
|9,171 |
|||
|9,218 |
|||
|9,310 |
|||
|9,403 |
|||
|'''9,979''' |
|||
|'''18,640''' |
|||
|'''50.4%''' |
|||
|- |
|||
|Eleonora Gullone ([[Animal Justice Party|AJP]]) |
|||
|2.3% |
|||
|837 |
|||
|860 |
|||
|891 |
|||
|928 |
|||
|999{{Xmark}} |
|||
| colspan="3" |''Eliminated'' |
|||
|- |
|||
|Alan Walker ([[Family First Party|FFP]]) |
|||
|0.8% |
|||
|282 |
|||
|283 |
|||
|295{{Xmark}} |
|||
| colspan="5" |''Eliminated'' |
|||
|- |
|||
|Jason Goldsmith ([[Independent (politician)|IND]]) |
|||
|0.7% |
|||
|247 |
|||
|263 |
|||
|316 |
|||
|349{{Xmark}} |
|||
| colspan="4" |''Eliminated'' |
|||
|- |
|||
|Steve Stefanopoulos ([[Independent (politician)|IND]]) |
|||
|0.6% |
|||
|227 |
|||
|241{{Xmark}} |
|||
| colspan="6" |''Eliminated'' |
|||
|- |
|||
|Alan Menadue ([[Independent (politician)|IND]]) |
|||
|0.2% |
|||
|82{{Xmark}} |
|||
| colspan="7" |''Eliminated'' |
|||
|- |
|||
!Total |
|||
|'''100%''' |
|||
|'''37,003''' |
|||
|} |
|||
===2009 Burlington mayoral election=== |
|||
===Canada=== |
|||
{{See also|2009 Burlington mayoral election}} |
|||
More often called the Alternative Vote in Canada,<ref>{{cite web|url=http://www.irpp.org/en/po/votes-and-seats/alternative-voting-or-mixed-memberproportional-what-can-we-expect/ |title=Alternative voting of mixed-member proportional: What can we expect? Louis Massicotte, University of Montreal |publisher=Policy Options |date=July–August 2001 |accessdate=23 April 2014}}</ref> IRV has never been used for federal elections but was used for provincial elections in [[List of British Columbia general elections|British Columbia]] (1952 and 1953), [[List of Alberta general elections|Alberta]] (1926), and [[List of Manitoba general elections|Manitoba]] (1927–1953).<ref>{{cite web|url=http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=285372 |title=The Political Consequences of the Alternative Vote: Lessons from Western Canada. Harold J. Jansen, University of Lethbridge |publisher=Canadian Journal of Political Science Vol. 37, Issue 03. pp 647-669 |date=September 2004 |accessdate=23 April 2014}}</ref> |
|||
{| class=wikitable style="text-align:right; float:right; margin-left:1em" |
|||
|+ Burlington mayoral election, 2009 (round-by-round analysis of votes) |
|||
|- |
|||
!colspan=2 |Candidates |
|||
!colspan=2 |1st round |
|||
!colspan=2 |2nd round |
|||
!colspan=2 |3rd round |
|||
|- |
|||
!'''Candidate''' |
|||
!Party |
|||
!Votes |
|||
!± |
|||
!Votes |
|||
!± |
|||
!Votes |
|||
!± |
|||
|- {{Party shading/Vermont Progressive}} |
|||
| style="text-align:left;"| '''[[Bob Kiss]]''' |
|||
| style="text-align:left;"| [[Vermont Progressive Party|Progressive]] |
|||
| 2585 |
|||
| +2585 |
|||
| 2981 |
|||
| +396 |
|||
| '''4313''' |
|||
| +1332 |
|||
|- {{Party shading/Republican}} |
|||
| style="text-align:left;"| Kurt Wright |
|||
| style="text-align:left;"| [[Vermont Republican Party|Republican]] |
|||
| '''2951''' |
|||
| +2951 |
|||
| '''3294''' |
|||
| +343 |
|||
| 4061 |
|||
| +767 |
|||
|- {{Party shading/Democratic}} |
|||
| style="text-align:left;"| Andy Montroll |
|||
| style="text-align:left;"| [[Vermont Democratic Party|Democrat]] |
|||
| 2063 |
|||
| +2063 |
|||
| 2554 |
|||
| +491 |
|||
| 0 |
|||
| −2554 |
|||
|- {{Party shading/Independent}} |
|||
| style="text-align:left;"| Dan Smith |
|||
| style="text-align:left;"| [[Independent (politician)|Independent]] |
|||
| 1306 |
|||
| +1306 |
|||
| 0 |
|||
| −1306 |
|||
|- |
|||
! style="text-align:left;" | Others |
|||
| |
|||
| 71 |
|||
| +71 |
|||
| 0 |
|||
| −71 |
|||
|- |
|||
! style="text-align:left;" | [[Exhausted ballot|Exhausted]] |
|||
| |
|||
| 4 |
|||
| +4 |
|||
| 151 |
|||
| +147 |
|||
| 606 |
|||
| +455 |
|||
|} |
|||
Under Burlington, Vermont's second-ever IRV mayoral election in 2009, the winner, Bob Kiss, was elected over the more popular Andy Montroll as a result of a first-round spoiler effect. |
|||
[[FairVote]] touted the 2009 election as one of its major success stories,<ref name=":4">{{Cite news |last=Etnier |first=Carl |date=6 March 2009 |title=Instant runoff was success |url=https://www.rutlandherald.com/articles/instant-runoff-was-success/ |access-date=17 March 2018 |work=Rutland Herald }}{{Dead link|date=September 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> claiming it helped the city save on costs of a traditional runoff<ref name=":4" /><ref name=":5">{{Cite news |last=Totten |first=Shay |title=Burlington Residents Seek Repeal of Instant Runoff Voting |url=https://www.sevendaysvt.com/vermont/burlington-residents-seek-repeal-of-instant-runoff-voting/Content?oid=2177125 |access-date=17 March 2018 |work=Seven Days |language=en |quote=We waited to bring in the signatures because we didn't want this to be about Kurt Wright losing after being ahead, or Andy Montroll who had more first and second place votes and didn't win. We wanted this to be about IRV.}}</ref> and prevented a [[spoiler effect]],<ref name=":02">{{Cite web |last=Bouricius |first=Terry |date=17 March 2009 |title=Response to Faulty Analysis of Burlington IRV Election |url=http://www.fairvote.org/response-to-faulty-analysis-of-burlington-irv-election |access-date=1 October 2017 |website=FairVote.org |quote=successfully prevented the election of the candidate who would likely have won under plurality rules, but would have lost to either of the other top finishers in a runoff}}</ref> although later analysis showed that without Wright in the election, Montroll would have defeated Kiss in a one-on-one race.<ref name=":10">{{Cite journal |last=Lewyn |first=Michael |date=2012 |title=Two Cheers for Instant Runoff Voting |journal=Phoenix L. Rev. |language=en |volume=6 |page=117 |ssrn=2276015 |quote=election where Democratic candidate for mayor was Condorcet winner but finished third behind Republican and 'Progressive{{'-}}}}</ref> |
|||
IRV is used to elect the leaders of two of the largest federal political parties in Canada, the [[Liberal Party of Canada]]<ref>{{cite web|url=https://www.liberal.ca/newsroom/party-news/liberals-vote-overwhelmingly-in-favour-of-one-member-one-vote-2/ |title=Liberals vote overwhelmingly in favour of one-member, one-vote |publisher=Liberal.ca |date=2 May 2009 |accessdate=17 April 2011}}</ref> and the [[Conservative Party of Canada]]. The [[New Democratic Party of Canada]] uses a mixture of IRV and [[exhaustive voting]], depending on the member. Canadian Prime Minister [[Stephen Harper]] won an IRV election to become party leader in the [[Conservative Party of Canada leadership election, 2004|2004 leadership election]]. In 2013, the Liberal Party picked Justin Trudeau with IRV in a national primary.<ref>{{cite web|url=http://www2.macleans.ca/2013/04/05/the-liberal-leadership-vote-who-what-where-when-how-could-it-go-wrong/|title=What Comes Next in the Liberal Vote |publisher=Maclean's |date=5 April 2013 |accessdate=17 April 2013}}</ref> |
|||
[[Mathematicians]] and [[Voting theory|voting theorists]] criticized the election results as revealing several [[Pathological (mathematics)|pathologies]] associated with instant-runoff voting, noting that Kiss was elected as a result of 750 votes [[Participation criterion|cast against him]] (ranking Kiss in last place).<ref>{{Cite journal |last1=Felsenthal |first1=Dan S. |last2=Tideman |first2=Nicolaus |date=2014 |title=Interacting double monotonicity failure with direction of impact under five voting methods |journal=Mathematical Social Sciences |volume=67 |pages=57–66 |doi=10.1016/j.mathsocsci.2013.08.001 |issn=0165-4896 |quote=A display of non-monotonicity under the Alternative Vote method was reported recently, for the March 2009 mayoral election in Burlington, Vermont.}}</ref><ref name=":8">{{Cite journal |last1=Ornstein |first1=Joseph T. |last2=Norman |first2=Robert Z. |date=1 October 2014 |title=Frequency of monotonicity failure under Instant Runoff Voting: estimates based on a spatial model of elections |journal=Public Choice |language=en |volume=161 |issue=1–2 |pages=1–9 |doi=10.1007/s11127-013-0118-2 |issn=0048-5829 |s2cid=30833409 |quote=Although the Democrat was the Condorcet winner (a majority of voters preferred him in all two way contests), he received the fewest first-place votes and so was eliminated ... 2009 mayoral election in Burlington, VT, which illustrates the key features of an upward monotonicity failure}}</ref> |
|||
The province of [[Ontario]] has announced that they will allow [[List of municipalities in Ontario|municipalities]] the option to use instant-runoff voting for local elections starting in 2018.<ref>{{cite web|url=http://www.thestar.com/news/queenspark/2014/09/30/ranked_ballot_a_priority_for_2018_civic_elections_kathleen_wynne_says.html |title=Ranked ballot a priority for 2018 civic elections, Kathleen Wynne says |publisher=The Toronto Star |date=30 Sep 2014 |accessdate=30 Sep 2014}}</ref> |
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Several [[electoral reform]] advocates branded the election a failure after Kiss was elected, despite 54 percent of voters voting for Montroll over Kiss,<ref>{{Cite journal |last1=Bristow-Johnson |first1=Robert |date=2023 |title=The failure of Instant Runoff to accomplish the purpose for which it was adopted: a case study from Burlington Vermont |journal=Constitutional Political Economy |volume=34 |issue=3 |pages=378–389 |doi=10.1007/s10602-023-09393-1}}</ref> violating the principle of [[Condorcet winner|majority rule]].<ref name=":10" /><ref>{{Cite book |last=Ellenberg |first=Jordan |url=https://archive.org/details/hownottobewrongp0000elle |title=How Not to Be Wrong: The Power of Mathematical Thinking |date=29 May 2014 |publisher=Penguin |isbn=9780698163843 |page=[https://archive.org/details/hownottobewrongp0000elle/page/385 385] |language=en |quote=a majority of voters liked the centrist candidate Montroll better than Kiss, and a majority of voters liked Montroll better than Wright ... yet Montroll was tossed in the first round. |url-access=registration}}</ref><ref>{{Cite SSRN |last=Stensholt |first=Eivind |date=7 October 2015 |title=What Happened in Burlington? |ssrn=2670462 |quote=K was elected even though M was a clear Condorcet winner and W was a clear Plurality winner.}}</ref><ref name=":6">{{Cite news |last=Dopp |first=Kathy |date=10 June 2009 |title=IRV much worse than old runoffs |url=https://www.aspentimes.com/news/irv-much-worse-than-old-runoffs/ |access-date=17 March 2018 |work=The Aspen Times |language=en}}</ref> |
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=== Czech Republic === |
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IRV is used to elect leaders of the [[Green Party (Czech Republic)|Green party]].<ref>{{cite web|author=Václav Novák|url=http://data.blog.ihned.cz/c1-59414520-zeleni-otestovali-volebni-system-bez-ztracenych-hlasu-ktery-podporuje-sirokou-shodu|title=Zelení otestovali volební systém bez ztracených hlasů, který podporuje širokou shodu|publisher=http://data.blog.ihned.cz|date=28 February 2013|accessdate=30 December 2013}}</ref> |
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<!-- Lint |
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===Hong Kong=== |
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{{Election box ranked choice candidate with party link|party=Vermont Progressive Party|candidate=[[Bob Kiss]]|maxround=3|maxvotes=4313|maxvotespercent=48.0|r1votes=2585|fullwidthvotes=4500}} |
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IRV is used to elect a small number of functional constituencies of the Legislative Council, all of which have very small electorates. |
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{{Election box ranked choice candidate with party link|party=Vermont Republican Party|candidate=Kurt Wright|maxround=3|maxvotes=4061|maxvotespercent=45.2|r1votes=2951|fullwidthvotes=4500}} |
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{{Election box ranked choice candidate with party link|party=Vermont Democratic Party|candidate=Andy Montroll|maxround=2|maxvotes=2554|maxvotespercent=28.4|r1votes=2063|fullwidthvotes=4500}} |
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{{Election box ranked choice candidate with party link|party=Independent politician|candidate=Dan Smith|maxround=1|maxvotes=1306|maxvotespercent=14.5|r1votes=1306|fullwidthvotes=4500}} |
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{{Election box ranked choice candidate with party link|party=Green Party (United States)|candidate=James Simpson|maxround=1|maxvotes=35|maxvotespercent=0.4|r1votes=35|fullwidthvotes=4500}} |
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{{Election box ranked choice candidate with party not linked|party=Write-in|candidate=|maxround=1|maxvotes=36|maxvotespercent=0.4|r1votes=36|fullwidthvotes=4500}} |
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{{Election box ranked choice exhausted no party no change with bar|maxvotes=606|maxvotespercent=6.7|r1votes=4|fullwidthvotes=4500|votes=606|percentage=6.7}} |
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{{Election box ranked choice end}}--> |
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== |
== See also == |
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* [[Single transferable vote]], a proportional method that reduces to instant runoff in single-winner elections. |
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IRV is used in numerous [[electoral college]] environments, including the election of the [[President of India]] by the members of the [[Parliament of India]] and of the [[Vidhan Sabha]]s – the [[States and territories of India|state]] legislatures.<ref>{{cite web|author=swapnil |url=http://swapsushias.blogspot.com/2010/10/presidents-of-indiarashtrapati.html |title=IAS OUR DREAM: Presidents of India, Rashtrapati Bhavan, Trivia |publisher=Swapsushias.blogspot.com |date=29 October 2010 |accessdate=3 December 2010}}</ref> |
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* [[Ranked voting]] |
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* [[Comparison of voting rules|Comparison of electoral systems]] |
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* [[Alternative vote plus]] (AV+), or alternative vote top-up, proposed by the [[Jenkins Commission (UK)|Jenkins Commission]] in the UK |
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* [[Duverger's law]] |
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* [[Write-in candidate]] |
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== |
== Notes == |
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{{notelist}} |
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While most [[elections in the Republic of Ireland]] use the [[single transferable vote]] (STV),<ref>{{cite web|url=http://www.environ.ie/en/LocalGovernment/Voting/PublicationsDocuments/FileDownLoad,1895,en.pdf|title=Guide to Ireland’s PR-STV Electoral System|last=Franchise Section|date=February 2011|publisher=Department of the Environment, Heritage and Local Government|accessdate=29 April 2011}}</ref> in single-winner contests this reduces to IRV.<ref name="Muckerras">{{cite journal|last=Muckerras|first=Malcolm|author2=William Muley|year=1998|title=Preferential Voting in Australia, Ireland and Malta|journal=Griffith Law Review|volume=7|issue=2|pages=225–248|url=http://kirra.austlii.edu.au/au/journals/GriffLawRw/1998/14.pdf}}</ref> This is the case in all [[Irish presidential election|Presidential elections]]<ref name="Muckerras"/> and [[Seanad panel]] by-elections,<ref name="panelact1947">[http://www.irishstatutebook.ie/1947/en/act/pub/0042/sec0058.html Seanad Electoral (Panel Members) Act, 1947 §58: Provision applicable where more than one casual vacancy.] Irish Statute Book</ref> and most [[List of Irish by-elections|Dáil by-elections]]<ref name="Muckerras"/> In the rare event of multiple simultaneous vacancies in a single [[Dáil constituency]], a single STV by-election may be held;<ref>[http://www.irishstatutebook.ie/1992/en/act/pub/0023/sec0039.html Electoral Act, 1992 §39(3)] Irish Statute Book</ref> for Seanad panels, multiple IRV by-elections are held.<ref name="panelact1947"/> |
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===New Zealand=== |
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IRV is used in the elections of [[mayor]]s and councillors in single-member wards in some New Zealand cities, such as Dunedin and Wellington. Multi-member wards in these cities use STV.<ref name="Elections - 2007 Final Results"/> |
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IRV, under the name Alternative Vote, was one of the four alternative systems available (alongside [[Mixed member proportional representation|MMP]], [[Single transferable vote|STV]] and [[Supplementary member|SM]]) in the [[Electoral reform in New Zealand|1992 referendum on the voting method]] to elect MP's to the [[New Zealand House of Representatives]]. It came third of the alternative systems (ahead of SM) with 6.6% of the vote. IRV, under the name Preferential Vote, was one of the four alternative systems choices presented in the [[New Zealand voting method referendum, 2011|2011 voting method referendum]], but the referendum resulted in New Zealanders choosing to keep their proportional system of representation instead, while IRV came last with 8.34%. |
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===Papua New Guinea=== |
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Since 2003, the national parliament of [[Papua New Guinea]] has been elected using an IRV variant called Limited Preferential Voting, where voters are limited to ranking three candidates.<ref>{{cite web|url=http://archive.fairvote.org/articles/papuanewguinea.htm |title=Center for Voting and Democracy |publisher=Archive.fairvote.org |accessdate=17 April 2011}}</ref><ref>{{cite web|url=http://aceproject.org/ero-en/regions/pacific/PG/Papua_new_guinea_leaflet.pdf/view |title=Limited Preferential Voting |publisher=Aceproject.org |accessdate=3 October 2010}}</ref> |
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===United Kingdom=== |
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In the United Kingdom the system is commonly known as the alternative vote. It is used to elect the leaders of the [[Labour Party (UK)|Labour Party]] and the [[Liberal Democrats]]. (The leader of the [[Conservative Party (UK)|Conservative Party]] is elected under a similar system, a variant of the [[exhaustive ballot]].) It is also used for [[by elections to the House of Lords|by-elections to the British House of Lords]], in which [[hereditary peer]]s are selected for that body.<ref name="Notice of Conservative Hereditary Peers' By-Election to the House of Lords">{{cite web| url = http://www.parliament.uk/documents/lords-information-office/holnotice20100601.pdf |title = Notice of Conservative Hereditary Peers' By-Election to the House of Lords |publisher=House of Lords}}</ref> AV is also used by members of parliament to elect the chairmen of select committees and the [[Speaker of the House of Lords]]. The Speaker of the House of Commons is elected by the exhaustive ballot. |
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In 2010, the Conservative—Liberal Democrat coalition government agreed to hold a [[United Kingdom Alternative Vote referendum, 2011|national referendum on the alternative vote]],<ref>{{cite news|url=http://news.bbc.co.uk/2/hi/uk_news/politics/election_2010/8675848.stm |title=BBC's Q&A: The Conservative-Lib Dem coalition |publisher=BBC |date=13 May 2010 |accessdate=3 October 2010}}</ref> held on 5 May 2011.<ref>{{cite news|author=Norman Smith Chief political correspondent, BBC Radio 4 |url=http://news.bbc.co.uk/1/hi/politics/10483841.stm |title=Voting reform referendum planned for next May |publisher=BBC|date=2 July 2010 |accessdate=3 October 2010}}</ref> The proposal would have affected the way in which [[Members of Parliament]] are elected to the [[House of Commons (United Kingdom)|British House of Commons]] at Westminster. The [[Results of the United Kingdom Alternative Vote referendum, 2011|result of the referendum]] was a vote against adoption of the alternative vote by a margin of 67.9 percent to 32.1 percent.<ref>[http://ukreferendumresults.aboutmyvote.co.uk/en/default.aspx The Electoral Commission] Referendum result</ref> |
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===United States=== |
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{{main|Instant-runoff voting in the United States}} |
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IRV is used by several jurisdictions in the United States, including [[San Francisco]]<ref name=mpr20090510/> and [[Oakland, California]],<ref name=or2010/> and [[Minneapolis]] and [[Saint Paul, Minnesota]].<ref name=mpr20090510/> United States private associations that use IRV<ref name="Organizations & Corporations"/> include the [[Hugo Award]]s for science fiction,<ref name="Oscars Copy Hugos"/> the [[Academy of Motion Picture Arts and Sciences]] in selection of the Oscar for Best Picture,<ref name="www.oscars.org"/> and more than fifty colleges and universities for student elections.<ref>instantrunoff.com</ref> |
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==Similar systems== |
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===Runoff voting=== |
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The term ''instant runoff voting'' is derived from the name of a class of voting systems called runoff voting. In runoff voting voters do not rank candidates in order of preference on a single ballot. Instead a similar effect is achieved by using multiple rounds of voting. All multi-round runoff voting systems allow voters to change their preferences in each round, incorporating the results of the prior round to influence their decision. This is not possible in IRV, as participants vote only once, and this prohibits certain forms of [[tactical voting]] that can be prevalent in 'standard' runoff voting. |
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===Exhaustive ballot=== |
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A system closer to IRV is the [[exhaustive ballot]]. In this system—one familiar to fans of the television show [[American Idol]]—one candidate is eliminated after each round, and many rounds of voting are used, rather than just two.<ref>{{cite web|url=http://www.securevote.com.au/gloss_of_terms.html#e |title=Glossary: Exhaustive ballot |publisher=Securevote.com.au |accessdate=6 May 2010}}</ref> Because holding many rounds of voting on separate days is generally expensive, the exhaustive ballot is not used for large-scale, public elections. |
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===Two-round systems=== |
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The simplest form of runoff voting is the [[two-round system]], which typically excludes all but two candidates after the first round, rather than gradually eliminating candidates over a series of rounds. Eliminations can occur with or without allowing and applying preference votes to choose the final two candidates. A second round of voting or counting is only necessary if no candidate receives an overall majority of votes. This system is used in France and the Finnish presidential election. |
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===Contingent vote=== |
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[[File:IRV-toptwo flowchart.png|thumb|Top-two IRV]] |
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The [[contingent vote]], also known as '''Top-two IRV''', or ''batch-style'', is the same as IRV except that if no candidate achieves a majority in the first round of counting, all but the two candidates with the most votes are eliminated, and the second preferences for those ballots are counted. As in IRV, there is only one round of voting. |
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Under a variant of contingent voting used in [[Sri Lanka]], and the elections for [[Mayor of London]] in the United Kingdom, voters rank a specified maximum number of candidates. In London, the [[Supplementary Vote]] allows voters to express first and second preferences only. Sri Lankan voters [[Contingent vote#contingent vote in Sri Lanka|rank up to three candidates]] for the [[President of Sri Lanka]]. |
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While similar to "sequential-elimination" IRV, top-two can produce different results. Excluding more than one candidate after the first count might eliminate a candidate who would have won under sequential elimination IRV. Restricting voters to a maximum number of preferences is more likely to exhaust ballots if voters do not anticipate which candidates will finish in the top two. This can encourage voters to vote more [[tactical voting|tactically]], by ranking at least one candidate they think is likely to win. |
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Conversely, a practical benefit of 'contingent voting' is expediency and confidence in the result with only two rounds. Particularly in elections with few (e.g., fewer than 100) voters, numerous ties can destroy confidence. Heavy use of tie-breaking rules leaves uncomfortable doubts over whether the winner might have changed if a recount had been performed. |
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===Larger runoff process=== |
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IRV may also be part of a larger runoff process: |
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* Some jurisdictions that hold runoff elections allow absentee (only) voters to submit IRV ballots, because the interval between votes is too short for a second round of absentee voting. IRV ballots enable absentee votes to count in the second (general) election round if their first choice does not make the runoff. [[Arkansas]], [[South Carolina]] and [[Springfield, Illinois]] adopt this approach.<ref>{{cite web|url=http://www.electionline.org/Portals/1/Publications/SC.EAP.2006primary.pdf |title=Initiatives – Pew Center on the States |publisher=Electionline.org |accessdate=6 May 2010}}</ref> Louisiana uses it only for members of the United States Service or who reside overseas.<ref>{{Citation |
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| title =IRV for Lousiana's Overseas Voters |
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| type =web page |
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| publisher =FairVote IRV America |
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| url =http://archive.fairvote.org/?page=1669 |
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| accessdate =June 16, 2013}}</ref> |
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* IRV can quickly eliminate weak candidates in early rounds of an [[exhaustive ballot]] runoff, using rules to leave the desired number of candidates for further balloting. |
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* IRV allows an arbitrary victory threshold in a single round of voting, e.g., 60%. In such cases a second vote may be held to confirm the winner.<ref>For example, in 2006, the [[Independence Party of Minnesota]] used IRV for its endorsement elections, requiring 60% to win, and ''exhaustive balloting'' to follow if needed.</ref> |
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* IRV elections that require a majority of cast ballots but not that voters rank all candidates may require more than a single IRV ballot due to exhausted ballots. |
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* Robert's Rules recommends [[Ranked voting systems|preferential voting]] for elections by mail and requiring a majority of cast votes to elect a winner, giving IRV as their example. For in-person elections, they recommend repeated balloting until one candidate receives an absolute majority of all votes cast. Repeated voting allows voters to turn to a candidate as a compromise who polled poorly in the initial election.<ref name="autogenerated1"/> |
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The common feature of these IRV variations is that one vote is counted per ballot per round, with rules that eliminate the weakest candidate(s) in successive rounds. Most IRV implementations drop the "[[majority]] of cast ballots" requirement.<ref>[http://www.leg.state.vt.us/docs/2004/bills/intro/S-022.HTM Vermont S.22 1(c)3] Sec. 7. (6) ... if neither of the last two remaining candidates in an election ... received a majority, the report and the tabulations performed by the instant runoff count committee shall be forwarded to the Washington superior court, which shall issue a certificate of election to whichever of the two remaining candidates received the greatest number of votes at the conclusion of the instant runoff tabulation, and send a certified copy of the tabulation and results to the secretary of state.</ref> |
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==See also== |
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* [[Alternative Vote Plus (AV+)]] or Alternative Vote Top-up proposed by the [[Jenkins Commission (UK)]] |
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* [[First-past-the-post voting]] |
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* [[None of the above]] (NOTA) or [[None of the above#Re-open Nominations (RON)|Re-Open Nominations]] (RON) |
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* [[Outline of democracy]] |
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* [[Single transferable vote]], AV system for elections with multiple positions to be filled |
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==References== |
==References== |
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{{Reflist |
{{Reflist}} |
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==External links== |
==External links== |
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* [https://electionlab.mit.edu/research/instant-runoff-voting# "Explainer: Instant runoff voting"] by [[MIT Election Science Lab]] |
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* 2010 articles from the [http://www.re-constitution.org.uk/news/articles/37/ Constitution Society] and [http://www.electoral-reform.org.uk/article.php?id=55 Electoral Reform Society] summarizing the proposed change in the United Kingdom to IRV/Alternative Vote |
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{{voting methods}} |
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===Practice=== |
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* [http://aceproject.org/ace-en/topics/es/esd/esd01/esd01d/esd01d01 Advantages and disadvantages of AV] from the [http://www.aceproject.org/ ACE Project] Electoral Design Reference Materials |
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* [http://www.idea.int/publications/esd/index.cfm A Handbook of Electoral System Design] from [http://www.idea.int/ International IDEA] |
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* [http://www.aec.gov.au/ Australian Electoral Commission Web Site] |
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* [http://www.australianpolitics.com/elections/features/preferential.shtml Preferential Voting in Australia] from Australian Politics.com |
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* [http://www.sfgov2.org/index.aspx?page=599 San Francisco Department of Elections, California] |
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* [http://www.acgov.org/rov/rcv/ Alameda County Registrar of Voters, California] |
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* [http://www.ci.minneapolis.mn.us/elections/rcv.asp City of Minneapolis, Minnesota] |
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* [http://www.ncsbe.gov/sampleballots/2010General/0GDURH04.pdf State of North Carolina] |
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===Demos and simulations=== |
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* [http://apps.startribune.com/news/20130915-ranked-choice-voting/ The Star Tribune: How ranked-choice voting works] – an interactive graphic |
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* [http://www.americanquorum.com AmericanQuorum.com] A ranked choice ballot tool from the Indaba Application Network, including the animated display of an instant runoff. |
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* [http://news.bbc.co.uk/1/hi/uk_politics/8506306.stm BBC: Would the alternative vote have changed history?, illustration of how the results of the last six general elections might have looked had the 'alternative vote' system been in place.] |
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* [http://www.openstv.org/ OpenSTV – Open source software for computing IRV and STV] |
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* [http://www.demochoice.org/dcballot.php?poll=Futurama1 ''Favourite Futurama Character Poll''] |
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* [http://zesty.ca/voting/sim/ Voting System Visualizations] – 2-dimensional plots of results of various systems, with assumptions of sincere voting behavior. |
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* [http://bolson.org/voting/essay.html Simulation Of Various Voting Models for Close Elections] Opposition article by Brian Olson. |
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===Advocacy groups and positions=== |
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* [http://www.yestofairervotes.org/ Yes to Fairer Votes ] campaign site for the Yes side of the [[United Kingdom Alternative Vote referendum, 2011]] |
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* [http://www.washingtonpost.com/opinions/district-should-adopt-instant-runoff-elections/2013/04/24/71c581e2-ad19-11e2-b6fd-ba6f5f26d70e_story.html Washington Post] |
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* [http://www.fairvote.org/instant-runoff-voting Instant Runoff Voting] at [[FairVote]] |
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* [http://www.lwvofvt.org/files/position_on_voter_rights_and_government.pdf League of Women Voters of Vermont] |
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* [http://instantrunoff.com/ InstantRunoff.com] |
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* [http://www.123toronto.ca/main.htm Ranked Ballot Initiative of Toronto, Canada] |
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* [http://www.rooseveltcampusnetwork.org/policy/instant-runoff-voting-national-elections Roosevelt Institution] |
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* [http://www.voterchoicema.org/ Citizens for Voter Choice :: Massachusetts] |
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* [http://www.fairvotemn.org/ FairVote Minnesota] |
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* [http://www.commoncause.org/site/pp.asp?c=dkLNK1MQIwG&b=4849119 Common Cause Massachusetts] |
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* [http://www.brookings.edu/papers/2007/0228electionreform_Opp08.aspx/ Brookings Institution's "Empowering Moderate Voters" paper] |
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* [http://blogs.abc.net.au/antonygreen/2011/02/does-the-alternative-vote-bring-tyranny-to-australia.html Does the Alternative Vote Bring Tyranny to Australia? - Antony Green ABC] |
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===Opposition groups and positions=== |
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* [http://www.fairvote.ca/files/AV-backgrounder-august2009_1.pdf Fair Vote Canada paper] on the Alternative Vote |
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* [http://www.rangevoting.org/rangeVirv.html IRV page] at the [[Center for Range Voting]] |
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* [http://www.ncvoter.net/downloads/Instant_Runoff_Voting_Value_and_Risks_Report.pdf Instant Runoff Voting Report] Values and Risks Report by the N.C. Coalition for Verified Voting |
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{{voting systems}} |
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{{Parliament of Australia}} |
{{Parliament of Australia}} |
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{{United Kingdom Alternative Vote referendum, 2011}} |
{{United Kingdom Alternative Vote referendum, 2011}} |
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{{DEFAULTSORT:Instant-Runoff Voting}} |
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[[Category:Instant-runoff voting| ]] |
[[Category:Instant-runoff voting| ]] |
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[[Category:Non-monotonic electoral systems]] |
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[[Category:Preferential electoral systems]] |
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[[Category:Single-winner electoral systems]] |
[[Category:Single-winner electoral systems]] |
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[[Category:Preferential electoral systems]] |
Latest revision as of 23:31, 24 December 2024
A joint Politics and Economics series |
Social choice and electoral systems |
---|
Mathematics portal |
Instant-runoff voting (IRV) (US: ranked-choice voting (RCV), AU: preferential voting, UK: alternative vote) is a single-winner, multi-round elimination rule that uses ranked voting to simulate a series of runoffs with only one vote. In each round, the candidate with the fewest votes counting towards them is eliminated, and the votes are transferred to their next available preference until one of the options reaches a majority of the remaining votes. Instant runoff falls under the plurality-with-elimination family of voting methods,[1] and is thus closely related to rules like the exhaustive ballot and two-round runoff system.[2][3]
IRV has found some use in national elections in several countries, predominantly in the Anglosphere. It is used to elect members of the Australian House of Representatives and the National Parliament of Papua New Guinea as well as the President of India, the President of Ireland, and the President of Sri Lanka.
The rule was first developed and studied by the Marquis de Condorcet, who came to reject it after discovering it could eliminate the majority-preferred candidate in a race (today often called a Condorcet winner).[4][5][6] IRV is known to exhibit other mathematical pathologies, which include non-monotonicity[7] and the no-show paradox.[8][9] Like some other commonly-used systems, IRV also exhibits a kind of independence of irrelevant alternative violation called a center squeeze,[10][11] which may sometimes prevent the election of a Condorcet winner. Whilst the Marquis de Condorcet early on showed that it did not satisfy his Condorcet winner criterion, which it may fail under certain scenarios, instant-runoff voting satisfies many other majoritarian criteria, such as the majority criterion, mutual majority criterion and the Condorcet loser criterion.
Advocates have argued these properties are positive, because voting rules should encourage candidates to focus on their core support or political base, rather than building a broad coalition.[12] They also note that in countries like the United Kingdom without primaries or runoff elections, IRV can prevent spoiler effects by eliminating minor-party candidates in early rounds, and that unlike plurality, it is not affected by the presence of duplicate candidates (clones).
Election procedure
[edit]In instant-runoff voting, as with other ranked voting rules, each voter orders candidates from first to last. The counting procedure is then as follows:
- If there is a candidate that has a majority of the top preferences of the valid, active ballots, then that candidate is elected and the count stops. If not, go to step 2.
- If there is more than one candidate left, eliminate the one with the fewest top preferences.[a]
- Reassign votes held by the eliminated candidate(s) to the highest available preference indicated on each ballot paper (setting aside any with no remaining preferences). Return to Step 1.
It is possible for a candidate to win an instant-runoff race without any support from more than half of voters, even when there is an alternative majority-approved candidate; this occurs when some voters truncate their ballots to show they do not support any candidates in the final round.[13] In practice, candidates who do not receive a majority of votes in the first round usually do not finish with a majority.[14]
Properties
[edit]Wasted votes and Condorcet winners
[edit]Compared to a plurality voting system that rewards only the top vote-getter, instant-runoff voting mitigates the problem of wasted votes.[15] However, it does not ensure the election of a Condorcet winner, which is the candidate who would win a direct election against any other candidate in the race.
Invalid, incomplete and exhausted ballots
[edit]All forms of ranked-choice voting reduce to plurality when all ballots rank only one candidate. By extension, ballots for which all candidates ranked are eliminated are equivalent to votes for any non-winner in plurality, and considered exhausted ballots.
Some political scientists have found the system contributes to higher rates of spoiled votes,[16] partly because the ballot marking is more complex.[16][14] Most jurisdictions with IRV do not require complete rankings and may use columns to indicate preference instead of numbers. In American elections with IRV, more than 99 percent of voters typically cast a valid ballot.[17]
A 2015 study of four local US elections that used IRV found that inactive ballots occurred often enough in each of them that the winner of each election did not receive a majority of votes cast in the first round. The rate of inactive ballots in each election ranged from a low of 9.6 percent to a high of 27.1 percent.[18]
Resistance to strategy
[edit]Instant-runoff voting has notably high resistance to tactical voting but less to strategic nomination.
Party strategizing and strategic nomination
[edit]In Australia, preference deals (where one party's voters agree to place another party's voters second, in return for their doing the same) between parties are common. Parties and candidates often encourage their supporters to participate in these preference deals using How-to-vote cards explaining how to use their lower rankings to maximize the chances of their ballot helping to elect someone in the preference deal before it may exhaust.[19]
Instant runoff may be manipulable via strategic candidate entry and exit, reducing similar candidates' chances of winning. Such manipulation does not need to be intentional, instead acting to deter candidates from running in the first place.[20] Spatial model simulations indicate that instant runoff rewards strategic withdrawal by candidates.[21][b]
Tactical voting
[edit]Gibbard's theorem demonstrates that no (deterministic, non-dictatorial) voting method can be entirely immune from tactical voting. This implies that IRV is susceptible to tactical voting in some circumstances. In particular, when there exists a Condorcet winner who IRV fails to elect, voters who prefer the Condorcet winner to the IRV winner have an incentive to use the compromising strategy.[21]: proposition 17 IRV is also sometimes vulnerable to a paradoxical strategy of ranking a candidate higher to make them lose, due to IRV failing the monotonicity criterion.[22]
Research suggests that IRV is very resistant to tactical voting. In a test of multiple methods, instant runoff was found to be the second-most-resistant to tactical voting, after a class of instant runoff-Condorcet hybrids.[23] IRV is also completely immune to the burying strategy: ranking a strong opposition candidate lower can't get one's preferred candidate elected.[21]: proposition 3
Tactical voting in IRV seeks to alter the order of eliminations in early rounds, to ensure that the original winner is challenged by a stronger opponent in the final round. For example, in a three-party election where voters for both the left and right prefer the centrist candidate to stop the opposing candidate from winning, those voters who care more about defeating the opposition than electing their own candidate may cast a tactical first-preference vote for the centrist candidate.
Spoiler effect
[edit]Proponents of IRV claim that IRV eliminates the spoiler effect, since IRV makes it safe to vote honestly for marginal parties. Under a plurality method, voters who sympathize most strongly with a marginal candidate are strongly encouraged to instead vote for a more popular candidate who shares some of the same principles, since that candidate has a much greater chance of being elected and a vote for the marginal candidate will not result in the marginal candidate's election. An IRV method reduces this problem, since the voter can rank the marginal candidate first and the mainstream candidate second; in the likely event that the fringe candidate is eliminated, the vote is not wasted but is transferred to the second preference.
However, when the third-party candidate is more competitive, they can still act as a spoiler under IRV,[24][25][26] by taking away first-choice votes from the more mainstream candidate until that candidate is eliminated, and then that candidate's second-choice votes helping a more-disliked candidate to win. In these scenarios, it would have been better for the third party voters if their candidate had not run at all (spoiler effect), or if they had voted dishonestly, ranking their favourite second rather than first (favorite betrayal).[27][better source needed] This is the same bracketing effect exploited by Robinette and Tideman in their research on strategic campaigning, where a candidate alters their campaign to cause a change in voter honest choice, resulting in the elimination of a candidate who nevertheless remains more preferred by voters.
For example, in the 2009 Burlington, Vermont, mayoral election, if the Republican candidate who lost in the final instant runoff had not run, the Democratic candidate would have defeated the winning Progressive candidate. In that sense, the Republican candidate was a spoiler—albeit for an opposing Democrat, rather than some political ally—even though leading in first choice support.[26] This also occurred in the 2022 Alaska's at-large congressional district special election. If Republican Sarah Palin, who lost in the final instant runoff, had not run, the more centrist Republican candidate, Nick Begich, would have defeated the winning Democratic candidate, Mary Peltola.[28]
Reception
[edit]The system has had a mixed reception among political scientists and social choice theorists.[29][30] Some have suggested that the system does not do much to decrease the impact of wasted votes relative to plurality.[31][16][32] Research has found IRV causes lower confidence in elections[33][34][35] and does not substantially affect minority representation,[36] voter turnout,[29][32] or long-run electoral competition.[29][36] Opponents have also noted a high rate of repeals for the system.[34]
Voter confusion and legitimacy
[edit]Governor Paul LePage[37] and Representative Bruce Poliquin[38] claimed, ahead of the 2018 primary elections, that IRV would result in "one person, five votes", as opposed to "one person, one vote". Federal judge Lance Walker rejected these claims, and the 1st circuit court denied Poliquin's emergency appeal.[39]
Similarity to plurality
[edit]Often instant-runoff voting elections are won by the candidate who leads in first-count vote tallies so they choose the same winner as first-past-the-post voting would have. In Australia federal elections, the 1972 election had the largest number of winners who would not have won under first past the post but still only 14 out of 125 seats filled were not won by the first-count leader.[40]
Participation
[edit]The effect of IRV on voter turnout is difficult to assess. In a 2021 report, researchers at New America, a think tank based in Washington, D. C., said it may increase turnout by attracting more and more diverse candidates, but the impact would be realized most significantly by getting rid of the need for primaries.[41] The overall impact on diversity of candidates is difficult to detect.[29]
Terminology
[edit]While instant run-off voting is distinguished from its multiple winner equivalent, the single transferable vote, in most English-speaking discussion of electoral systems, no distinction between the two is made in Ireland, one of the few countries to use these systems in all elections, either by the general population or in legal texts. The Constitution of Ireland describes the electoral system as "proportional representation by means of the single transferable vote"[42], as do all other statutory authorities, when referring to either single-winner or multiple-winner elections. The acronym "PR-STV" is in general use to describe both types of elections. Examples of single-winner elections in Ireland which are described officially as "proportional representation by means of the single transferable vote" are the election of the President and the election of the Ceann Comhairle (chairperson of Dáil Éireann). The lack of distinction between the systems in Ireland reflects that there is no difference in the mechanics of the process from election to election, only the number of candidates to be elected by that process. This is not always the case when discussing the systems in the abstract, as there are many variations in how such elections could be run.
Instant-runoff voting derives its name from the way the ballot count simulates a series of runoffs, similar to an exhaustive ballot system, except that voters do not need to turn out several times to vote.[43] It is also known as the alternative vote, transferable vote, ranked-choice voting (RCV), single-seat ranked-choice voting, or preferential voting (but use of some of those terms may lead to misunderstanding as they also apply to STV.)[44]
Britons and New Zealanders generally call IRV the "alternative vote" (AV).[45][46] Australians, who use IRV for most single winner elections, call IRV "preferential voting".[47] While this term is widely used by Australians, it is somewhat of a misnomer. Depending on how "preferential" is defined, the term would include all voting systems, apply to any system that uses ranked ballots (thus both IRV and STV), or would exclude IRV (IRV fails positive responsiveness because ballot markings are not interpreted as "preferences" in the traditional sense. Under IRV (and STV), secondary preferences are used as back-up preferences/contingency votes).
Jurisdictions in the United States such as San Francisco, Minneapolis, Maine, and Alaska have tended to use the term "ranked-choice voting" in their laws that apply to IRV contests. The San Francisco Department of Elections claimed the word "instant" in the term "instant-runoff voting" could confuse voters into expecting results to be immediately available.[48][49] As a result of American influence, the term ranked-choice voting is often used in Canada as well.[50] American NGO FairVote has promoted the terminology "ranked-choice voting" to refer to IRV,[50][51] a choice that has caused controversy and accusations that the organization is attempting to obscure the existence of other ranked-choice methods that could compete with IRV.[citation needed]
IRV is occasionally referred to as Hare's method[52] (after Thomas Hare) to differentiate it from other ranked-choice voting methods such as majority-choice voting, Borda, and Bucklin, which use weighted preferences or methods that allow voter's lower preference to be used against voter's most-preferred choice.
When the single transferable vote (STV) method is applied to a single-winner election, it becomes IRV; the government of Ireland has called IRV "proportional representation" based on the fact that the same ballot form is used to elect its president by IRV and parliamentary seats by proportional representation (STV), but IRV is a non-proportional winner-take-all (single-winner) election method, while STV elects multiple winners.[53]
State law in South Carolina[54] and Arkansas[55] use "instant runoff" to describe the practice of having certain categories of absentee voters cast ranked-choice ballots before the first round of an election and counting those ballots in any subsequent runoff elections.
History and use
[edit]History
[edit]This method was first discussed by the Marquis de Condorcet in 1788, who quickly rejected it after showing it would often eliminate a candidate preferred by a majority of voters.[5][56]
IRV was later independently reinvented by Thomas Hare (of England) and Carl Andrae (of Denmark) in the form of the single transferable vote. Henry Richmond Droop then proposed applying the system to single-winner contests. (He also invented the Droop quota, which equates to a simple majority in a single-winner contest.)
Global use
[edit]National level elections
[edit]Country | Body or office | Type of body or office | Electoral system | Total seats | Notes |
---|---|---|---|---|---|
Australia | House of Representatives | Lower chamber of legislature | IRV | 151 | |
Ireland | President | Head of State | IRV | ||
Dáil Éireann | Lower chamber of legislature | Single transferable vote (STV), by-elections using IRV | 158[57] | ||
Papua New Guinea | National Parliament | Unicameral legislature | IRV | 109 | |
United States | President (via Electoral College) | Head of State and Government | Alaska and Maine use IRV to select the state's electoral college seat winner or winners. In Maine, 2 electors are allocated to the winner of the state vote plurality and the others (currently 2) are allocated by plurality in each congressional district. In Alaska, the winner gets all Electoral College electors of the state (as Alaska has only one at-large district, the effect is the same). | 7 EVs[58] (out of 538) | |
House of Representatives | Lower chamber of legislature | IRV in Maine
Nonpartisan primary system with IRV in the second round (among top four candidates) in Alaska.[59][60][61][62] |
3 (out of 435) | ||
Senate | Upper chamber of legislature | 4 (out of 100) |
Robert's Rules of Order
[edit]In the United States, the sequential elimination method used by IRV is described in Robert's Rules of Order Newly Revised as an example of ranked-choice voting that can be used to elect officers.[63] Robert's Rules note that ranked-choice systems (including IRV) are an improvement on simple plurality but recommend against runoff-based rules because they often prevent the emergence of a consensus candidate with broad support. The book instead recommends repeated balloting until some candidate manages to win a majority of votes. Two other books on American parliamentary procedure, The Standard Code of Parliamentary Procedure[64] and Riddick's Rules of Procedure,[65] take a similar stance.
Similar methods
[edit]Runoff voting
[edit]This section possibly contains original research. (August 2024) |
The term instant-runoff voting is derived from the name of a class of voting methods called runoff voting. In runoff voting voters do not rank candidates in order of preference on a single ballot. Instead a similar effect is achieved by using multiple rounds of voting. All multi-round runoff voting methods allow voters to change their preferences in each round, incorporating the results of the prior round to influence their decision, which is not possible in IRV.
The runoff method closest to IRV is the exhaustive ballot. In this method—familiar to fans of the television show American Idol—one candidate is eliminated after each round, and many rounds of voting are used, rather than just two. Because holding many rounds of voting on separate days is generally expensive, the exhaustive ballot is not used for large-scale, public elections.
A more practical form of runoff voting is the two-round system, which excludes all but the top-two candidates after the first round, rather than gradually eliminating candidates over a series of rounds. Eliminations can occur with or without allowing and applying preference votes to choose the final two candidates. A second round of voting or counting is only necessary if no candidate receives an overall majority of votes. This method is used in Mali, France and the Finnish and Slovenian presidential election.
Contingent vote
[edit]This section possibly contains original research. (August 2024) |
The contingent vote, also known as "top-two IRV", is the same as IRV, except that if no candidate achieves a majority in the first round of counting, all but the two candidates with the most votes are eliminated, and the second preferences for those ballots are counted. As in IRV, there is only one round of voting.
Under a variant of contingent voting used in Sri Lanka, and formerly for the elections for Mayor of London in the United Kingdom, voters rank a specified maximum number of candidates. In London, the supplementary vote allowed[c] voters to express first and second preferences only. Sri Lankan voters rank up to three candidates to elect the president of Sri Lanka.
While similar to "sequential-elimination" IRV, top-two can produce different results. Excluding more than one candidate after the first count might eliminate a candidate who would have won under sequential elimination IRV. Restricting voters to a maximum number of preferences is more likely to exhaust ballots if voters do not anticipate which candidates will finish in the top two. This can encourage voters to vote more tactically, by ranking at least one candidate they think is likely to win.
Conversely, a practical benefit of 'contingent voting' is expediency and confidence in the result with only two rounds.
Larger runoff process
[edit]IRV may also be part of a larger runoff process:
- Some jurisdictions that hold runoff elections allow absentee (only) voters to submit IRV ballots, because the interval between votes is too short for a second round of absentee voting. IRV ballots enable absentee votes to count in the second (general) election round if their first choice does not make the runoff. Arkansas, South Carolina and Springfield, Illinois adopt this approach.[66] Louisiana uses it only for members of the United States Service or who reside overseas.[67][better source needed][needs update]
- IRV can quickly eliminate weak candidates in early rounds of an exhaustive ballot runoff, using rules to leave the desired number of candidates for further balloting.
- IRV elections that require a majority of cast ballots but not that voters rank all candidates may require more than a single IRV ballot due to exhausted ballots.
- Robert's Rules recommends preferential voting for elections by mail and requiring a majority of cast votes to elect a winner. For in-person elections, they recommend repeated balloting until one candidate receives an absolute majority of all votes cast; if candidates drop out as soon as it becomes clear they cannot win, this procedure will always elect a Condorcet winner. The use of repeated balloting allows voters to resolve Condorcet cycles by discussion and compromise, or by electing a consensus candidate who might have polled poorly in the initial election.[63]
Comparison to first-past-the-post
[edit]In the Australian federal election in September 2013, 135 out of the 150 House of Representatives seats (or 90 percent) were won by the candidate who led on first preferences. The other 15 seats (10 percent) were won by the candidate who placed second on first preferences.[68][better source needed]
Variations
[edit]A number of IRV methods, varying as to ballot design and as to whether or not voters are obliged to provide a full list of preferences, are in use in different countries and local governments.
In an optional preferential voting system, voters can give a preference to as many candidates as they wish. They may make only a single choice, known as "bullet voting", and some jurisdictions accept a single box marked with an "X" (as opposed to a numeral "1") as valid for the first preference. This may result in exhausted ballots, where all of a voter's preferences are eliminated before a candidate is elected, such that the "majority" in the final round may only constitute a minority fraction of all ballots cast. Optional preferential voting is used for elections for the President of Ireland as well as some elections in New South Wales and Queensland.[69][70]
In a full-preferential voting method, voters are required to mark a preference for every candidate standing.[71] Ballots that do not contain a complete ordering of all candidates are in some jurisdictions considered spoilt or invalid, even if there are only two candidates standing. This can become burdensome in elections with many candidates and can lead to "donkey voting", in which some voters simply choose candidates at random or in top-to-bottom order, or a voter may order his or her preferred candidates and then fill in the remainder on a donkey basis. Full preferential voting is used for elections to the Australian federal parliament and for most state parliaments.
Other methods only allow marking preferences for a maximum of the voter's top three favourites, a form of partial preferential voting.[72]
A version of instant-runoff voting applying to the ranking of parties was first proposed for elections in Germany in 2013[73] as spare vote.[citation needed]
Voting method criteria
[edit]As shown by Arrow, Gibbard, and others, it's usually impossible for a method to pass all of a number of seemingly reasonable properties, or criteria, at once. IRV is no exception: it passes some and fails others. The following criteria are satisfied and failed by IRV:
Satisfied criteria
[edit]Condorcet loser Criterion
[edit]The Condorcet loser criterion states that "if a candidate would lose a head-to-head competition against every other candidate, then that candidate must not win the overall election". IRV (like all voting methods with a final runoff round) meets this criterion, since the Condorcet loser cannot win a runoff.
Independence of clones criterion
[edit]The independence of clones criterion states that "the election outcome remains the same even if an identical candidate who is equally preferred decides to run". Advocates have noted that IRV meeting this criterion[74][75] greatly reduces the impact of clones compared to FPTP.
Later-no-harm criterion
[edit]The later-no-harm criterion states that "if a voter alters the order of candidates lower in his/her preference (e.g. swapping the second and third preferences), then that does not affect the chances of the most preferred candidate being elected". Instant runoff satisfies this criterion.
Majority criterion
[edit]The majority criterion states that "if one candidate is preferred by an absolute majority of voters, then that candidate must win". Instant runoff also satisfies this criterion.
Mutual majority criterion
[edit]The mutual majority criterion states that "if an absolute majority of voters prefer every member of a group of candidates to every candidate not in that group, then one of the preferred group must win". Note that this is satisfied because when all but one candidate that a mutual majority prefer is eliminated, the votes of the majority all flow to the remaining candidate, in contrast to FPTP, where the majority would be treated as separate small groups. Instant runoff satisfies this criterion as well.
Resolvability criterion
[edit]The resolvability criterion states that "the probability of an exact tie must diminish as more votes are cast".[citation needed]
Failed criteria
[edit]This section possibly contains original research. (September 2024) |
Condorcet winner criterion
[edit]The Condorcet winner criterion states that "if a candidate would win a head-to-head competition against every other candidate, then that candidate must win the overall election". It is incompatible with the later-no-harm criterion, so IRV does not meet this criterion.
IRV is more likely to elect the Condorcet winner than plurality voting and traditional runoff elections. The California cities of Oakland, San Francisco and San Leandro in 2010 provide an example; there were a total of four elections in which the plurality-voting leader in first-choice rankings was defeated, and in each case the IRV winner was the Condorcet winner, including a San Francisco election in which the IRV winner was in third place in first choice rankings.
A particularly notable Condorcet failure occurred in the 2009 Burlington mayoral election.
Independence of irrelevant alternatives
[edit]The independence of irrelevant alternatives criterion states that "the election outcome remains the same even if a candidate who cannot win decides to run." Instant-runoff voting violates this. In the general case, instant-runoff voting can be susceptible to strategic nomination: whether or not a candidate decides to run at all can affect the result even if the new candidate cannot themselves win. This is less likely to happen than under plurality, but much more likely than under the Minimax Condorcet method.[21]
Monotonicity criterion
[edit]The monotonicity criterion says that a voter ranking a candidate higher on their ballot should not cause that candidate to lose and conversely, that a voter ranking a candidate lower on their ballot should not help that candidate win. The exact probability of a monotonicity failure depends on the circumstances, but with 3 major candidates, the probabilities range from 15 percent under the impartial culture model[76]: Table 6 to 8.5 percent in the case of a strict left–right spectrum.[77]
Participation criterion
[edit]The participation criterion says that candidates should not lose as a result of having "too many voters"—a set of ballots that all rank A>B should not switch the election winner from B to A. IRV fails this criterion. In his 1984 study, mathematician Depankar Ray found that in elections where IRV elects a different candidate from plurality, that there was an estimated 50 percent probability that some voters would have gotten a more preferable outcome if they had not participated.[9]
Reversal symmetry criterion
[edit]The reversal symmetry criterion states that the first- and last-place candidates should switch places if every ballot is reversed. In other words, it should not matter whether voters rank candidates from best-to-worst and select the best candidate, or whether they rank them worst-to-best and then select the least-bad candidate.
IRV fails this criterion: it is possible to construct an election where reversing the order of every ballot does not alter the final winner; that is, the first- and last-place finishers, according to IRV, are the same candidate.[78]
Comparison to other voting systems
[edit]Criterion Method |
Majority winner | Majority loser | Mutual majority | Condorcet winner |
Condorcet loser | Smith |
Smith-IIA |
IIA/LIIA |
Cloneproof | Monotone | Participation | Later-no-harm |
Later-no-help |
No favorite betrayal |
Ballot
type | |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
First-past-the-post voting | Yes | No | No | No | No | No | No | No | No | Yes | Yes | Yes | Yes | No | Single mark | |
Anti-plurality | No | Yes | No | No | No | No | No | No | No | Yes | Yes | No | No | Yes | Single mark | |
Two round system | Yes | Yes | No | No | Yes | No | No | No | No | No | No | Yes | Yes | No | Single mark | |
Instant-runoff | Yes | Yes | Yes | No | Yes | No | No | No | Yes | No | No | Yes | Yes | No | Ranking | |
Coombs | Yes | Yes | Yes | No | Yes | No | No | No | No | No | No | No | No | Yes | Ranking | |
Nanson | Yes | Yes | Yes | Yes | Yes | Yes | No | No | No | No | No | No | No | No | Ranking | |
Baldwin | Yes | Yes | Yes | Yes | Yes | Yes | No | No | No | No | No | No | No | No | Ranking | |
Tideman alternative | Yes | Yes | Yes | Yes | Yes | Yes | Yes | No | Yes | No | No | No | No | No | Ranking | |
Minimax | Yes | No | No | Yes |
No | No | No | No | No | Yes | No | No |
No | No | Ranking | |
Copeland | Yes | Yes | Yes | Yes | Yes | Yes | Yes | No | No | Yes | No | No | No | No | Ranking | |
Black | Yes | Yes | No | Yes | Yes | No | No | No | No | Yes | No | No | No | No | Ranking | |
Kemeny–Young | Yes | Yes | Yes | Yes | Yes | Yes | Yes | LIIA Only | No | Yes | No | No | No | No | Ranking | |
Ranked pairs | Yes | Yes | Yes | Yes | Yes | Yes | Yes | LIIA Only | Yes | Yes | No |
No | No | No | Ranking | |
Schulze | Yes | Yes | Yes | Yes | Yes | Yes | Yes | No | Yes | Yes | No |
No | No | No | Ranking | |
Borda | No | Yes | No | No | Yes | No | No | No | No | Yes | Yes | No | Yes | No | Ranking | |
Bucklin | Yes | Yes | Yes | No | No | No | No | No | No | Yes | No | No | Yes | No | Ranking | |
Approval | Yes | No | No | No | No | No | No | Yes |
Yes | Yes | Yes | No | Yes | Yes | Approvals | |
Majority Judgement | No | No |
No |
No | No | No | No | Yes |
Yes | Yes | No |
No | Yes | Yes | Scores | |
Score | No | No | No | No | No | No | No | Yes |
Yes | Yes | Yes | No | Yes | Yes | Scores | |
STAR | No | Yes | No | No | Yes | No | No | No | No | Yes | No | No | No | No | Scores | |
Random ballot |
No | No | No | No | No | No | No | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Single mark | |
Sortition |
No | No | No | No | No | No | No | Yes | No | Yes | Yes | Yes | Yes | Yes | None | |
Table Notes |
|
Examples
[edit]The first example is a fictional one for the purpose of demonstrating the principle of instant runoff. The other examples are drawn from the results of real-life elections.
Tennessee capital example
[edit]
Suppose that Tennessee is holding an election on the location of its capital. The population is concentrated around four major cities. All voters want the capital to be as close to them as possible. The options are:
- Memphis, the largest city, but far from the others (42% of voters)
- Nashville, near the center of the state (26% of voters)
- Chattanooga, somewhat east (15% of voters)
- Knoxville, far to the northeast (17% of voters)
The preferences of each region's voters are:
42% of voters Far-West |
26% of voters Center |
15% of voters Center-East |
17% of voters Far-East |
---|---|---|---|
|
|
|
|
It takes three rounds to determine a winner in this election.
Round 1 – In the first round no city gets a majority:
Votes in round/
City Choice |
1st |
---|---|
Memphis | 42% |
Nashville | 26% |
Knoxville | 17% |
Chattanooga | 15% |
If one of the cities had achieved a majority vote (more than half), the election would end there. If this were a first-past-the-post election, Memphis would win because it received the most votes. But IRV does not allow a candidate to win on the first round without having an absolute majority of the active votes. Since no city has won yet, the city with the least first-place support (Chattanooga) is eliminated from consideration. The ballots that listed Chattanooga as first choice are added to the totals of the second-choice selection on each ballot.
Round 2 – In the second round of tabulation, Chattanooga's 15% of the total votes have been added to the second choices selected by the voters for whom that city was first-choice (in this example Knoxville):
Votes in round/
City Choice |
1st | 2nd |
---|---|---|
Memphis | 42% | 42% |
Nashville | 26% | 26% |
Knoxville | 17% | 32% |
Chattanooga | 15% |
In the first round, Memphis was first, Nashville was second and Knoxville was third. With Chattanooga eliminated and its votes redistributed, the second round finds Memphis still in first place, followed by Knoxville in second and Nashville has moved down to third place. No city yet has secured a majority of votes, so the now last placed Nashville is eliminated and the ballots currently counting for Nashville are added to the totals of Memphis or Knoxville based on which city is ranked next on that ballot.
Round 3
As Memphis and Knoxville are the only two cities remaining in the contest, this round will be the final round. In this example the second-choice of the Nashville voters is Chattanooga, which is already eliminated. Therefore, the votes are added to their third-choice: Knoxville. The third round of tabulation yields the following result:
Votes in round/
City Choice |
1st | 2nd | 3rd |
---|---|---|---|
Memphis | 42% | 42% | 42% |
Nashville | 26% | 26% | |
Knoxville | 17% | 32% | 58% |
Chattanooga | 15% |
Result: Knoxville, which was running third in the first tabulation, has moved up from behind to take first place in the third and final round. The winner of the election is Knoxville. However, if 6% of voters in Memphis were to put Nashville first, the winner would be Nashville, a preferable outcome for voters in Memphis. This is an example of potential tactical voting, though one that would be difficult for voters to carry out in practice. Also, if 17% of voters in Memphis were to stay away from voting, the winner would be Nashville. This is an example of IRV failing the participation criterion.
For comparison, note that traditional first-past-the-post voting would elect Memphis, even though most citizens consider it the worst choice, because 42% is larger than any other single city. As Nashville is a Condorcet winner, Condorcet methods would elect Nashville. A two-round method would have a runoff between Memphis and Nashville where Nashville would win, too.
1990 Irish presidential election
[edit]The 1990 Irish presidential election provides a simple example of how instant-runoff voting can produce a different result from first-past-the-post voting and prevent some spoiler effects associated with plurality voting. The three major candidates were Brian Lenihan of Fianna Fáil, Austin Currie of Fine Gael, and Mary Robinson of the Labour Party. After the first count, Lenihan had the largest share of first-choice rankings. Currie had the fewest votes and was eliminated. After this, Robinson received 82 percent of Currie's votes, thereby overtaking Lenihan.
Candidate | Round 1 | Round 2 | ||
---|---|---|---|---|
Mary Robinson | 612,265 | 38.9% | 817,830 | 51.6% |
Brian Lenihan | 694,484 | 43.8% | 731,273 | 46.2% |
Austin Currie | 267,902 | 16.9% | Eliminated | |
Exhausted ballots | 9,444 | 0.6% | 34,992 | 2.2% |
Total | 1,584,095 | 100% | 1,584,095 | 100% |
2014 Prahran election (Victoria)
[edit]Another real-life example of IRV producing results different from first-past-the-post can be seen in the 2014 Victorian general election in Prahran. In this rare instance, the candidate who initially placed third, (Greens candidate Sam Hibbins), won the seat.[80] In the 7th and final round, Hibbins narrowly defeated Liberal candidate Clem Newton-Brown by a margin of 277 votes.
Candidate | 1st | 2nd | 3rd | 4th | 5th | 6th | 7th | ||
---|---|---|---|---|---|---|---|---|---|
Clem Newton-Brown (LIB) | 44.8% | 16,582 | 16,592 | 16,644 | 16,726 | 16,843 | 17,076 | 18,363 | 49.6% |
Neil Pharaoh (ALP) | 25.9% | 9,586 | 9,593 | 9,639 | 9,690 | 9,758 | 9,948 | Eliminated | |
Sam Hibbins (GRN) | 24.8% | 9,160 | 9,171 | 9,218 | 9,310 | 9,403 | 9,979 | 18,640 | 50.4% |
Eleonora Gullone (AJP) | 2.3% | 837 | 860 | 891 | 928 | 999 | Eliminated | ||
Alan Walker (FFP) | 0.8% | 282 | 283 | 295 | Eliminated | ||||
Jason Goldsmith (IND) | 0.7% | 247 | 263 | 316 | 349 | Eliminated | |||
Steve Stefanopoulos (IND) | 0.6% | 227 | 241 | Eliminated | |||||
Alan Menadue (IND) | 0.2% | 82 | Eliminated | ||||||
Total | 100% | 37,003 |
2009 Burlington mayoral election
[edit]Candidates | 1st round | 2nd round | 3rd round | ||||
---|---|---|---|---|---|---|---|
Candidate | Party | Votes | ± | Votes | ± | Votes | ± |
Bob Kiss | Progressive | 2585 | +2585 | 2981 | +396 | 4313 | +1332 |
Kurt Wright | Republican | 2951 | +2951 | 3294 | +343 | 4061 | +767 |
Andy Montroll | Democrat | 2063 | +2063 | 2554 | +491 | 0 | −2554 |
Dan Smith | Independent | 1306 | +1306 | 0 | −1306 | ||
Others | 71 | +71 | 0 | −71 | |||
Exhausted | 4 | +4 | 151 | +147 | 606 | +455 |
Under Burlington, Vermont's second-ever IRV mayoral election in 2009, the winner, Bob Kiss, was elected over the more popular Andy Montroll as a result of a first-round spoiler effect.
FairVote touted the 2009 election as one of its major success stories,[81] claiming it helped the city save on costs of a traditional runoff[81][82] and prevented a spoiler effect,[83] although later analysis showed that without Wright in the election, Montroll would have defeated Kiss in a one-on-one race.[84]
Mathematicians and voting theorists criticized the election results as revealing several pathologies associated with instant-runoff voting, noting that Kiss was elected as a result of 750 votes cast against him (ranking Kiss in last place).[85][86]
Several electoral reform advocates branded the election a failure after Kiss was elected, despite 54 percent of voters voting for Montroll over Kiss,[87] violating the principle of majority rule.[84][88][89][90]
See also
[edit]- Single transferable vote, a proportional method that reduces to instant runoff in single-winner elections.
- Ranked voting
- Comparison of electoral systems
- Alternative vote plus (AV+), or alternative vote top-up, proposed by the Jenkins Commission in the UK
- Duverger's law
- Write-in candidate
Notes
[edit]- ^ This procedure can be sped-up by eliminating more than one candidate if their combined top preferences are less than the next-lowest remaining candidate; this process is sometimes called batch elimination. When batch elimination is used, the procedure can terminate if some candidate has a majority.
- ^ Figure 4 on page 137 shows instant-runoff voting having exit incentive despite being clone independent.
- ^ Following the Elections Act 2022, voting in mayoral elections now takes place under the first-past-the-post system.
References
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Candidates C and D spoiled the election for B ... With them in the running, A won, whereas without them in the running, B would have won. ... Instant runoff voting ... does not do away with the spoiler problem entirely, although it ... makes it less likely
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We waited to bring in the signatures because we didn't want this to be about Kurt Wright losing after being ahead, or Andy Montroll who had more first and second place votes and didn't win. We wanted this to be about IRV.
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successfully prevented the election of the candidate who would likely have won under plurality rules, but would have lost to either of the other top finishers in a runoff
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election where Democratic candidate for mayor was Condorcet winner but finished third behind Republican and 'Progressive'
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A display of non-monotonicity under the Alternative Vote method was reported recently, for the March 2009 mayoral election in Burlington, Vermont.
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Although the Democrat was the Condorcet winner (a majority of voters preferred him in all two way contests), he received the fewest first-place votes and so was eliminated ... 2009 mayoral election in Burlington, VT, which illustrates the key features of an upward monotonicity failure
- ^ Bristow-Johnson, Robert (2023). "The failure of Instant Runoff to accomplish the purpose for which it was adopted: a case study from Burlington Vermont". Constitutional Political Economy. 34 (3): 378–389. doi:10.1007/s10602-023-09393-1.
- ^ Ellenberg, Jordan (29 May 2014). How Not to Be Wrong: The Power of Mathematical Thinking. Penguin. p. 385. ISBN 9780698163843.
a majority of voters liked the centrist candidate Montroll better than Kiss, and a majority of voters liked Montroll better than Wright ... yet Montroll was tossed in the first round.
- ^ Stensholt, Eivind (7 October 2015). "What Happened in Burlington?". SSRN 2670462.
K was elected even though M was a clear Condorcet winner and W was a clear Plurality winner.
- ^ Dopp, Kathy (10 June 2009). "IRV much worse than old runoffs". The Aspen Times. Retrieved 17 March 2018.