simpson's paradox — free browser tool | fatcousin

aggregation can reverse every trend it contains · adjust group mix to see the reversal · runs locally

small stones

open surgery94.5%

PERC93.1%

winner: open surgery

large stones

open surgery81.9%

PERC86.7%

winner: PERC

combined (mix: 50% → small stones)

open surgery88.2%

PERC89.9%

combined winner: PERC ← PARADOX: reversal!

group mix

50%

aggregation creates a confounding variable · the mix of cases between groups drives the reversal · move the slider to watch it switch

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