The usage share of web browsers is the percentage of visitors to a group of websites that use a particular web browser. For example, when it is said that Internet Explorer has 66% usage share, it means that some version of Internet Explorer is used by 66% of visitors that visit a given set of sites.
Typically, the user agent string is used to identify which browser a visitor is using. The concept of browser percentages for the Web audience in general is sometimes called browser penetration.[citation needed]
Accuracy
Measuring browser usage in terms of the number of requests (page hits) made by each user agent can be misleading.
Overestimation
Not all requests are generated by a user, as a user agent can make requests at regular time intervals without user input. In this case, the usage of that user agent would then be overestimated. Some examples:
A web browser that refreshes the webpage at a regular time interval.
A feed reader that requests the RSS or Atom feed at a regular time interval.
Extra files like CSS hacks and JavaScript hacks are often sent to Internet Explorer.
Gecko-based browsers (such as Firefox) can prefetch linked web pages, potentially increasing hits. Link prefetching in Gecko-based browsers is used on pages with enhanced markup, including Google search results.[1]
A user who revisits a site shortly after changing or upgrading browsers may be double-counted under some methodologies; overall numbers at the time of a new version's release may be skewed.[2]
Certain anti-virus products fake their user-agent to appear to be popular browsers. This is done to trick attack sites that might display clean content to the scanner, but not to the browser. The Register reported in June 2008 that traffic from AVG Linkscanner, using an IE6 user-agent, outstripped human link clicks by nearly 10 to 1. [3]
Many types of software, such as Web validators or crawlers, fetch web pages, and send fictitious user-agent strings to appear more like normal traffic.
Underestimation
It is also possible to underestimate the usage share by using the number of requests, for example:
A graphical browser typically results in more hits than a text browser, as it downloads files referred to by the HTML document (e.g., images, CSS, and JavaScript).
Many browsers and download managers spoof a different user agent string to the web server to prevent erroneous or malicious browser sniffing which could result in receiving broken or incompatible code, or being completely blocked, and thus increasing the statistics for other browsers (as an example, prior to version 9, the Opera web browser had "Identify as Internet Explorer" as the default user setting)
Text-based and audio-based browsers do not download any webbugs at all.
Gecko-based browsers since Firefox 1.5 and Opera use fast Document Object Model (DOM) caching. JavaScript is only executed on pageload from net or disk cache, but not if it is loaded from DOM cache. This can have an impact on JavaScript based tracking of browser statistics.[4]
Some browser extensions and security programs (such as the popular Firefox extension NoScript) block javascript, flash, applets and some forms of HTML (HTML blocked through ClearClick) for non-whitelisted sites. This may also affect JavaScript based tracking of browser statistics.
Many browsers accessing a site via one proxy are apt to be counted as only one access, if the proxy caches the result; in particular, it is usual for browsers on mobile phones to access the web via proxies (many of which violate HTTP's specifications for proxies; even if a webbug is designed to work despite proxying, the proxies run by mobile operators may well mislead it).
While most browsers generate additional page hits by refreshing webpages when user navigates back through page history, some browsers (such as Opera) reuse cached content without resending requests to server.[5][6]
Generally, the more faithfully a browser implements HTTP's cache specifications, the more it shall be under-reported relative to browsers which implement those specifications poorly.[6]
On 2009-08-01, Net Applications began weighting its raw data based on the number of internet users in the countries concerned, using data from the CIA. The changes were applied retroactively to older data; the table below uses weighted data from 2007 Q4 onwards.[7]
Note: W3 Counter only lists the top 10 Browsers by Version. This is one of the reasons why Opera fluctuates between 0.7% and 1.2% in the table below, as some versions only make it into the top 10 occasionally. This site counts the last 25,000 page views from each site making relatively small sites contribute a lot more to the statistics than in an overall count.
As of July 31, 2009 uncategorised browsers are at 7.17%
Chuck Upsdell's Browser Stats lists web stats from many different stats sources and gives the approximate current usage share of the most popular layout engines.
StatCounter Global Stats tracks the market share of search engines, browsers and operating systems including mobile from over 4 billion monthly page views.
W3Schools' Browser Statistics lists the web stats only from the W3 Schools site, which gives the approximate usage share of browsers among "people with an interest for web technologies."
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