Representativeness heuristic

Psychological “rule-of-thumb” by which decisions are based upon how representative a particular case seems in reference to some class, group, or sequence of events – for example, judging the likelihood that a specific case belongs to a particular category, that is, an estimation about Instance A being a member of Category B.

When making comparisons between a phenomenon – a person, object, event, ideology, etc. – and our mental representation, a prototype or schema of the (projected) relevant category, strategies for moderating this bias include considering whether or to what extent our prototype in question might be inaccurate, biased, or incomplete, and noting people’s tendency to overestimate the degree of similarity between phenomena and categories, while consciously seeking and utilizing base rate information or other pertinent statistical information in reaching such judgements. We should recognize that our personal attitudes towards phenomena and prototypes, for example, bank tellers and whether they are more or less likely to hold a feminist outlook, biases such comparisons and subsequent judgements. 

†Representativeness bias
Any condition in which this cognitive strategy (above) for quickly estimating the probability that a given instance is a member of a particular category produces systematic errors.

(see also: Conjunction fallacy, Heuristics, Availability heuristic, Anchoring effect, Availability, Salience, Representativeness, Vividness)

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