Substitutability and similarity in binary choices

Abstract

The assumption that a binary choice probability is expressible as a monotone function of the scale values of the two alternatives is investigated. Four different conditions are shown to be equivalent forms of the same substitutability, or independence, principle which underlies most probabilistic theories of choice behavior. In a study of judgments of relative size, the independence principle is contrasted with the hypothesis that interstimulus similarity facilitates discrimination. The data reject the independence principle while supporting the similarity hypothesis.