Does the Dilution Effect Have a Conversational Basis?
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The dilution effect refers to the finding that judgments are often unduly influenced by nondiagnostic information, producing regressive judgment. The hypothesis of a conversational basis of the dilution effect, advanced in a recent study by Igou and Bless, holds that the effect reflects the operation of the conversational norm of relevance. A critique and reanalysis of their data yields only weak, if any, support for this conversational explanation. Furthermore, an experiment (n = 224) does not yield any supportive evidence, and a meta-analysis of available studies likewise supports the conclusion that the dilution effect occurs independently of the operation of conversational norms. However, consistent with a social-perceptual explanation, the experiment shows that the dilution effect occurs only for individuals high in personal need for structure. Although conversational norms do not provide the basis for the dilution effect, how they are involved in eliminating this reasoning error is discussed.