Look up base rates before forming a resemblance judgment

Before deciding "this looks like X," ask how common X actually is in the relevant population.

Why it works

Representativeness substitutes "how typical is this?" for "how probable is this?" — an easier question that feels like the right one. The substitution goes unnoticed because the resemblance judgment is computed automatically and feels like evidence. Anchoring on a base rate first forces the harder question to the front, making it much more likely that probability judgment is correctly calibrated rather than distorted by surface similarity.

How to do it

1. Name the category you’re about to assign something to ("this person is probably a doctor").
2. Before using resemblance as evidence, ask: "What fraction of people in the context I encountered this person are doctors?"
3. Write down that base rate as your starting probability.
4. Update for specific observed features only if those features are genuinely more common in the category than outside it.

Evidence

Kahneman and Tversky’s original 1973 research on the engineer/lawyer problem showed that subjects ignored explicit base rate information (70/30 split) when they had a representative description. Many follow-up studies replicate base-rate neglect, though instruction on base rates can partially correct it. (observational)

Base-rate neglect is stronger when the description is vivid and individuating; it reduces (but doesn’t vanish) when no description is given or when subjects are prompted to think like statisticians.

Sources

• Kahneman & Tversky (1973), On the psychology of prediction, Psychological Review

Common mistake

Treating resemblance as only one factor while still weighting it heavily — if you thought of the base rate at all but still landed on the representative answer, the heuristic won.