Judgment under Uncertainty: Heuristics and Biases

Abstract

This paper describes three heuristics, or mental operations, that are employed in judgment under uncertainty. (i) An assessment of representativeness or similarity, which is usually performed when people are asked to judge the probability that an object or event A belongs to a class or process B. (ii) An assessment of the availability of instances or scenarios, which is often employed when people are asked to assess the frequency of a class or the plausibility of a particular development. (iii) An adjustment from a starting point, which is usually employed in numerical prediction when a relevant value is available. These heuristics are highly economical and usually effective, but they lead to systematic and predictable errors. A better understanding of these heuristics and of the biases to which they lead could improve judgments and decisions in situations of uncertainty.

This article was published with minor modifications, in Science 185 (1974), 1124–1131, 27 September 1974. Copyright 1974 by the American Association for the Advancement of Science whose permission to reproduce it here is gratefully acknowledged.