Anchoring Base Rates April 7, 2012 I helped Joachim Krueger teach psychology at Brown after which he wrote this unifying post on pitting heuristics against each other: One of the most famous findings in the psychology of prediction is the phenomenon of base rate neglect. People mainly rely on judgments of representativeness. They assign an instance to the category whose prototype it resembles the most without regard to the relative size of the category. When the category is very small, the heuristic of representativeness leads to systematic overcategorization. Physicians overdiagnose rare diseases when the symptoms reflect the disease’s typical pattern, ordinary people overestimate the size of stereotyped minority groups, and scientific significance testers are too accepting of improbable alternatives to the null hypothesis.