Diagnosticity and the Base-Rate Effect.
DECISION RESEARCH EUGENE OR
Pagination or Media Count:
A common judgmental task involves predicting the category membership of an individual on the basis of information specific to that individual and background information regarding the base rate of different categories. According to statistical theory, predictions may deviate from base rates only to the extent that the individuating information is diagnostic. Previous research has demonstrated that diagnosticity is often judged by representativeness, the degree to which the individuating information is differentially suggestive of the different possible categories. Thus, information with high differential representativeness, even if it is worthless e.g., because its sources are unreliable, will swamp base-rate information. The present studies varied differential representativeness by manipulating the degree to which the prediction categories are similar to one another vis a vis the individuating information, and hence similarly represented by that individuating information. It was found that the effect of the base rate increased systematically as differential representativeness decreased. Representativeness was measured independently by several converging techniques. These measures predicted the magnitude of the base rate over entire sets of descriptions. Author