How Statistics Show Bias When It Doesn’t Exist -Mental Model 051

Simpson’s Paradox

A paradox in probability and statistics, in which a trend appears in different groups of data but disappears or reverses when these groups are combined.


Example: In 1973, graduate admissions to University of California, Berkeley, showed that men applying were more likely to be admitted than women. There appeared to be a gender bias.


But when examining the individual University departments, it appeared that six out of eighty-five departments were significantly biased against men, whereas only four were significantly biased against women. In fact, the pooled and corrected data showed a small but statistically significant bias in favor of women.


Wisdom: “Don’t cross a river if it is four feet deep on average.” ― Nassim Taleb


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