The Concept of Probability in Psychological Experiments

Volume 8 of the series Theory and Decision Library pp 25-48

Subjective Probability: A Judgment of Representativeness

  • Daniel KahnemanAffiliated withThe Hebrew University
  • , Amos TverskyAffiliated withThe Hebrew University

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This paper explores a heuristic — representativeness — according to which the subjective probability of an event, or a sample, is determined by the degree to which it: (i) is similar in essential characteristics to its parent population; and (ii) reflects the salient features of the process by which it is generated. This heuristic is explicated in a series of empirical examples demonstrating predictable and systematic errors in the evaluation of uncertain events. In particular, since sample size does not represent any property of the population, it is expected to have little or no effect on judgment of likelihood. This prediction is confirmed in studies showing that subjective sampling distributions and posterior probability judgments are determined by the most salient characteristic of the sample (e.g., proportion, mean) without regard to the size of the sample. The present heuristic approach is contrasted with the normative (Bayesian) approach to the analysis of the judgment of uncertainty.