Extension Neglect

Extension neglect is a cognitive bias in which people ignore the size of a sample, a set, or a scope, when that size is actually relevant to correctly interpreting the information, such as disregarding how many participants were included in a scientific study while still drawing conclusions from its reported results as though the sample size did not matter. The psychologists Daniel Kahneman and Amos Tversky described extension neglect as arising from a kind of judgment by prototype, in which a case is evaluated based on a representative example rather than on the full set it is drawn from, connecting it to the representativeness heuristic. Related patterns discussed under the same umbrella include base-rate neglect, insensitivity to sample size, scope neglect, duration neglect and the peak-end rule, and the effect is not universal, since presenting set-size information clearly can reduce or eliminate it in a given case.