MediumStatistics

Simpson’s Paradox

Two SigmaCitadel

A drug shows a higher recovery rate than placebo among men, and a higher recovery rate than placebo among women — yet a lower recovery rate overall when the groups are pooled. Explain precisely how this can happen, and give a concrete numeric example.

Approach

Give one group an easy base rate and one a hard base rate.

Then put most of the treated in the hard group.