Interrogate whether similarity is doing the work

When assessing probability or quality, ask whether you’re really judging similarity to a prototype.

Why it works

Representativeness substitutes "How much does this resemble the stereotype of X?" for "How probable is X?" The answer to the similarity question is vivid and accessible; the probability question requires base-rate retrieval and calculation. The result is that vivid resemblance can make unlikely outcomes feel probable (Linda the bank teller) and mute actual base-rate signals.

How to do it

1. When you form a probability judgment, ask: "Am I judging probability, or am I judging how much this fits the picture I have?"
2. List any ways the specific case diverges from the stereotype you’re comparing to.
3. Explicitly retrieve the base rate for this category before finalizing the probability estimate.

Evidence

Representativeness is one of Kahneman and Tversky’s core heuristics, demonstrated across many studies including the "Linda problem," which shows that people violate basic probability rules when a description is highly representative of a stereotype. Kahneman and Tversky (1973) showed the base-rate half of the same substitution: when a description resembled a prototype, predictions tracked the resemblance and all but ignored the prior probabilities they had been given. (observational)

Sources

• Tversky & Kahneman (1983), "Extensional vs. Intuitive Reasoning: The Conjunction Fallacy in Probability Judgment," Psychological Review
• Tversky, A., & Kahneman, D. (1983). Extensional versus intuitive reasoning: The conjunction fallacy in probability judgment. Psychological Review, 90(4), 293–315.
• Kahneman, D., & Tversky, A. (1973). On the psychology of prediction. Psychological Review, 80(4), 237–251.

Common mistake

Believing that more vivid or detailed descriptions are more informative about probability — additional details that fit the stereotype actually decrease the true probability while increasing the felt probability.