Representativeness Heuristic

The representativeness heuristic is a mental shortcut in which people judge the probability that something belongs to a category by how closely it resembles a typical, prototypical member of that category, rather than by considering the category's actual base rate. Psychologists Amos Tversky and Daniel Kahneman proposed the concept in the early 1970s, defining it as the degree to which an event is similar in its essential characteristics to the population it is drawn from and reflects the salient features of the process that generated it. The heuristic works by comparing a person, object or event against a stereotype or prototype already held in mind: someone dressed eccentrically and reading poetry in public, for instance, may be judged more likely to be a poet than an accountant because the image better matches the poet stereotype, even though accountants vastly outnumber poets in the population. While the shortcut can produce fast, often serviceable judgments, resemblance to a category does not actually establish a higher probability of membership in it, and relying on representativeness leads people to neglect base rate information and to make systematic errors, including the conjunction fallacy and the gambler's fallacy, both grounded in the same underlying heuristic.