Anscombe’s Quartet

I love simple examples that make an important point.  Anscombe’s quartet is a really great way to make the point that data visualization is critical to understand any statistical pattern.

For anyone who hasn’t seen it before: what do these four graphs have in common?

They have the same basic statistical properties:

Property Value
Mean of x in each case 9 (exact)
Sample variance of x in each case 11 (exact)
Mean of y in each case 7.50 (to 2 decimal places)
Sample variance of y in each case 4.122 or 4.127 (to 3 decimal places)
Correlation between x and y in each case 0.816 (to 3 decimal places)
Linear regression line in each case y = 3.00 + 0.500x (to 2 and 3 decimal places, respectively)

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