These are four x-y data sets, combined into a long format, which have the same traditional statistical properties (mean, variance, correlation, regression line, etc.). However, they look quite different.

quartets

Format

A data frame with 44 observations on the following 3 variables.

group

a categorical identifier for the quartet

x

a continuous variable

y

a continuous variable

Details

Data come default in R, but I elected to change the format to be a bit more accessible.

References

Anscombe, Francis J. (1973). "Graphs in Statistical Analysis." The American Statistician 27: 17–21.