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[[File:Anscombe's quartet 3.svg|right|425px|thumb|All four sets are identical when examined using simple summary statistics, but vary considerably when graphed]] |
[[File:Anscombe's quartet 3.svg|right|425px|thumb|All four sets are identical when examined using simple summary statistics, but vary considerably when graphed]] |
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'''Anscombe's quartet''' comprises four [[data set]]s that have nearly identical simple [[descriptive statistics]], yet have very different [[probability distribution|distributions]] and appear very different when [[Plot (graphics)|graphed]]. Each dataset consists of eleven [[Cartesian coordinate system|(''x'',''y'') points]]. They were constructed in 1973 by the [[statistician]] [[Francis Anscombe]] to demonstrate both the importance of graphing data when analyzing it, and the effect of [[outlier]]s and other [[influential observations]] on statistical properties. He described the article as being intended to counter the impression among statisticians that "numerical calculations are exact, but graphs are rough."<ref name="Anscombe">{{cite journal |last=Anscombe |first=F. J. |authorlink=Frank Anscombe |title=Graphs in Statistical Analysis |journal=[[American Statistician]] |volume=27 |year=1973 |issue=1 |pages=17–21 |jstor=2682899|doi=10.1080/00031305.1973.10478966}}</ref> |
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It has been rendered as an actual musical [[quartet]].<ref>{{Cite web|url= |
It has been rendered as an actual musical [[quartet]].<ref>{{Cite web|url=https://flat.io/score/60a8d8653374193bc2aa3633-anscombe-s-quartet|title = Anscombe's quartet - Sheet music for Violin, Viola, Cello}}</ref> |
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==Data== |
==Data== |
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Revision as of 19:35, 18 December 2021
Anscombe's quartet comprises four data sets that have nearly identical simple descriptive statistics, yet have very different distributions and appear very different when graphed. Each dataset consists of eleven (x,y) points. They were constructed in 1973 by the statistician Francis Anscombe to demonstrate both the importance of graphing data when analyzing it, and the effect of outliers and other influential observations on statistical properties. He described the article as being intended to counter the impression among statisticians that "numerical calculations are exact, but graphs are rough."[1] It has been rendered as an actual musical quartet.[2]
Data
For all four datasets:
| Property | Value | Accuracy |
|---|---|---|
| Mean of x | 9 | exact |
| Sample variance of x : s2 x |
11 | exact |
| Mean of y | 7.50 | to 2 decimal places |
| Sample variance of y : s2 y |
4.125 | ±0.003 |
| Correlation between x and y | 0.816 | to 3 decimal places |
| Linear regression line | y = 3.00 + 0.500x | to 2 and 3 decimal places, respectively |
| Coefficient of determination of the linear regression : | 0.67 | to 2 decimal places |
- The first scatter plot (top left) appears to be a simple linear relationship, corresponding to two variables correlated where y could be modelled as gaussian with mean linearly dependent on x.
- The second graph (top right) is not distributed normally; while a relationship between the two variables is obvious, it is not linear, and the Pearson correlation coefficient is not relevant. A more general regression and the corresponding coefficient of determination would be more appropriate.
- In the third graph (bottom left), the distribution is linear, but should have a different regression line (a robust regression would have been called for). The calculated regression is offset by the one outlier which exerts enough influence to lower the correlation coefficient from 1 to 0.816.
- Finally, the fourth graph (bottom right) shows an example when one high-leverage point is enough to produce a high correlation coefficient, even though the other data points do not indicate any relationship between the variables.
The quartet is still often used to illustrate the importance of looking at a set of data graphically before starting to analyze according to a particular type of relationship, and the inadequacy of basic statistic properties for describing realistic datasets.[3][4][5][6][7]
The datasets are as follows. The x values are the same for the first three datasets.[1]
| I | II | III | IV | ||||
|---|---|---|---|---|---|---|---|
| x | y | x | y | x | y | x | y |
| 10.0 | 8.04 | 10.0 | 9.14 | 10.0 | 7.46 | 8.0 | 6.58 |
| 8.0 | 6.95 | 8.0 | 8.14 | 8.0 | 6.77 | 8.0 | 5.76 |
| 13.0 | 7.58 | 13.0 | 8.74 | 13.0 | 12.74 | 8.0 | 7.71 |
| 9.0 | 8.81 | 9.0 | 8.77 | 9.0 | 7.11 | 8.0 | 8.84 |
| 11.0 | 8.33 | 11.0 | 9.26 | 11.0 | 7.81 | 8.0 | 8.47 |
| 14.0 | 9.96 | 14.0 | 8.10 | 14.0 | 8.84 | 8.0 | 7.04 |
| 6.0 | 7.24 | 6.0 | 6.13 | 6.0 | 6.08 | 8.0 | 5.25 |
| 4.0 | 4.26 | 4.0 | 3.10 | 4.0 | 5.39 | 19.0 | 12.50 |
| 12.0 | 10.84 | 12.0 | 9.13 | 12.0 | 8.15 | 8.0 | 5.56 |
| 7.0 | 4.82 | 7.0 | 7.26 | 7.0 | 6.42 | 8.0 | 7.91 |
| 5.0 | 5.68 | 5.0 | 4.74 | 5.0 | 5.73 | 8.0 | 6.89 |
It is not known how Anscombe created his datasets.[8] Since its publication, several methods to generate similar data sets with identical statistics and dissimilar graphics have been developed.[8][9] One of these, the Datasaurus Dozen, consists of points tracing out the outline of a dinosaur, plus twelve other data sets that have the same summary statistics.[10][11][12]
See also
- Exploratory data analysis
- Goodness of fit
- Regression validation
- Simpson's paradox
- Statistical model validation
References
- ^ a b Anscombe, F. J. (1973). "Graphs in Statistical Analysis". American Statistician. 27 (1): 17–21. doi:10.1080/00031305.1973.10478966. JSTOR 2682899.
- ^ "Anscombe's quartet - Sheet music for Violin, Viola, Cello".
- ^ Elert, Glenn (2021). "Linear Regression". The Physics Hypertextbook.
- ^ Janert, Philipp K. (2010). Data Analysis with Open Source Tools. O'Reilly Media. pp. 65–66. ISBN 978-0-596-80235-6.
- ^ Chatterjee, Samprit; Hadi, Ali S. (2006). Regression Analysis by Example. John Wiley and Sons. p. 91. ISBN 0-471-74696-7.
- ^ Saville, David J.; Wood, Graham R. (1991). Statistical Methods: The geometric approach. Springer. p. 418. ISBN 0-387-97517-9.
- ^ Tufte, Edward R. (2001). The Visual Display of Quantitative Information (2nd ed.). Cheshire, CT: Graphics Press. ISBN 0-9613921-4-2.
- ^ a b Chatterjee, Sangit; Firat, Aykut (2007). "Generating Data with Identical Statistics but Dissimilar Graphics: A follow up to the Anscombe dataset". The American Statistician. 61 (3): 248–254. doi:10.1198/000313007X220057. JSTOR 27643902. S2CID 121163371.
- ^ Matejka, Justin; Fitzmaurice, George (2017). "Same Stats, Different Graphs: Generating Datasets with Varied Appearance and Identical Statistics through Simulated Annealing". Proceedings of the 2017 CHI Conference on Human Factors in Computing Systems: 1290–1294. doi:10.1145/3025453.3025912. S2CID 9247543.
- ^ Murray, Lori L.; Wilson, John G. (April 2021). "Generating data sets for teaching the importance of regression analysis". Decision Sciences Journal of Innovative Education. 19 (2): 157–166. doi:10.1111/dsji.12233. ISSN 1540-4595. S2CID 233609149.
- ^ Andrienko, Natalia; Andrienko, Gennady; Fuchs, Georg; Slingsby, Aidan; Turkay, Cagatay; Wrobel, Stefan (2020), "Visual Analytics for Investigating and Processing Data", Visual Analytics for Data Scientists, Cham: Springer International Publishing, pp. 151–180, doi:10.1007/978-3-030-56146-8_5, ISBN 978-3-030-56145-1, S2CID 226648414, retrieved 2021-04-20
- ^ Matejka, Justin; Fitzmaurice, George (2017). "Same Stats, Different Graphs: Generating Datasets with Varied Appearance and Identical Statistics through Simulated Annealing". Autodesk Research. Retrieved 2021-04-20.
{{cite web}}: CS1 maint: url-status (link)
External links
- Department of Physics, University of Toronto
- Dynamic Applet made in GeoGebra showing the data & statistics and also allowing the points to be dragged (Set 5).
- Animated examples from Autodesk called the "Datasaurus Dozen".
- Documentation for the datasets in R.