Anscombe's Quartet
Anscombe's quartet

							

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The four datasets composing Anscombe's quartet.  All four sets have identical statistical parameters, but the graphs show them to be considerably different
Anscombe's quartet comprises four datasets 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]



For all four datasets:



Property

Value

Accuracy


Mean of x

9

exact


Sample variance of x: s2x

11

exact


Mean of y

7.50

to 2 decimal places


Sample variance of y: s2y

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 correlated variables, where y could be modelled as gaussian with mean linearly dependent on x.
For the second graph (top right), 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 modelled relationship 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.[2][3][4][5][6]
The datasets are as follows. The x values are the same for the first three datasets.[1]



Anscombe's quartet


Dataset I

Dataset II

Dataset III

Dataset 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.[7] Since its publication, several methods to generate similar datasets with identical statistics and dissimilar graphics have been developed.[7][8]
One of these, the Datasaurus dozen, consists of points tracing out the outline of a dinosaur, plus twelve other datasets that have the same summary statistics.[9][10][11]


Datasaurus dozen
Exploratory data analysis
Goodness of fit
Regression validation
Simpson's paradox
Statistical model validation


^ a b Anscombe, F. J. (1973). "Graphs in Statistical Analysis". American Statistician. 27 (1): 17–21. doi:10.1080/00031305.1973.10478966. JSTOR 2682899.

^ Elert, Glenn (2021). "Linear Regression". The Physics Hypertextbook. Archived from the original on 2020-10-01. Retrieved 2017-02-23.

^ 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. pp. 1290–1294. doi:10.1145/3025453.3025912. ISBN 9781450346559. S2CID 9247543.

^ Matejka, Justin; Fitzmaurice, George (2017). "Same Stats, Different Graphs: Generating Datasets with Varied Appearance and Identical Statistics through Simulated Annealing". Autodesk Research. Archived from the original on 2020-10-04. Retrieved 2021-04-20.

^ 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. Archived from the original on 2021-04-23. Retrieved 2021-04-20.

^ 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, archived from the original on 2024-10-03, retrieved 2021-04-20.



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.




