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Simpson's paradox

A compact thinking tool for spotting patterns and avoiding mistakes.

  1. The useful idea

    Simpson's paradox is a phenomenon in probability and statistics in which a trend appears in several groups of data but disappears or reverses when the groups are combined.

  2. How it works

    This result is often encountered in social science and medical science statistics, and is particularly problematic when frequency data are unduly given causal interpretations.

  3. Why it matters

    The paradox can be resolved when confounding variables and causal relations are appropriately addressed in the statistical modeling (e.g., through cluster analysis).

Use Simpson's paradox as a quick check before trusting your first conclusion.

Use Simpson's paradox as a quick check before trusting your first conclusion.

Test your recall

Which idea belongs to the explanation of Simpson's paradox?

  • Why it matters
  • How it works
  • The useful idea — correct

Simpson's paradox is a phenomenon in probability and statistics in which a trend appears in several groups of data but disappears or reverses when the groups are combined.

EvergreenLast verified 2026-07-19

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