Proceedings of the Annual Meeting of the Cognitive Science Society

This paper investigates a fundamental conflict in the literatureon people’s probability estimation. Research on ‘perception’of probability shows that people are accurate in their estimatesof probability of various simple events from samples. Equally,however, a large body of research shows that people’s probabil-ity estimates are fundamentally biased, and subject to reliableand striking fallacies in reasoning. We investigate this con-flict in an experiment that examines the occurrence of the con-junction fallacy in a probability perception task where peopleare asked to estimate the probability of simple and conjunc-tive events in a presented set of items. We find that people’sprobability estimates are accurate, especially for simple events,just as seen in previous studies. People’s estimates also showhigh rates of occurrence of the conjunction fallacy. We showhow this apparently contradictory result is consistent with arecent model of probability estimation, the probability theoryplus noise’ model.