Anscombe's Quartet
An illustration of the difficulty of data visualization where four datasets that have nearly identical simple descriptive statistics, can be made to appear very different when graphed.
EverydayConcepts.io
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Origin
They were constructed in 1973 by the statistician Francis Anscombe to demonstrate both the importance of graphing data before analyzing it and the effect of outliers 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."