Extension neglect

Extension neglect is a type of cognitive bias that occurs when the mind tends to ignore the size of the set during an evaluation in which the size of the set is logically relevant.

Extension neglect is described as being caused by judgment by prototype, of which the representativeness heuristic is a special case.

Forms of extension neglect include:

The extension effect is "neither universal nor absolute". If attention is drawn to set size in an easily interpretable way, an additive extension effect is reported, according to which the valuation of a set is a function of the valuation of a prototypical member of the set added to set size, rather than multiplied.