Base-Rate Neglect

Ignoring the underlying frequency of a category in favor of specific, individuating detail (often a stereotype or vivid story) when judging probability. The representativeness of the detail overrides the statistics.

Why it Matters

Plausible detail feels more diagnostic than dull base rates, so people draw confident conclusions that violate probability. Base rates should dominate when the detail is weak, yet they are routinely discarded.

Signals

• A detailed description swaying a probability judgment away from the obvious statistics.
• "It fits the profile, so it must be."
• Forgetting how rare the category actually is.

Benefits

Anchoring on the base rate first, then adjusting for the evidence, yields far better calibrated judgments.

Risks

Confident misclassification; diagnosing the rare and dramatic over the common and likely.

Tensions

Individuating evidence can be genuinely informative, but it is routinely overweighted against the base rate.

Examples

Assuming a quiet, bookish person is a librarian rather than a far more numerous salesperson; judging a candidate by a vivid anecdote instead of the success rate of similar candidates.