Extension neglect

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Extension neglect is a category of cognitive bias defined as appearing when "unless attention is specifically directed to it, the size of the set has little or no influence on its valuation"[1]

However, 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.[2]

Forms of extension neglect include:

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


  1. ^ Kaheman, Daniel (2000). "Evaluation by moments, past and future". In Daniel Kahneman and Amos Tversky (Eds.). Choices, Values and Frames. p. 708. 
  2. ^ Kahneman, 2000