THE COINCIDENCE EFFECT IN SIMILARITY AND CHOICE

Medin, Goldstone, and Markman (1995) recently described a series of pa rallel effects in similarity and choice. They suggested that similarit y and choice are related in a nontrivial way such that choice may enta il a similarity judgment to an explicit or constructed ideal. In this paper, the correspondences between similarity and choice were investig ated with respect to a phenomenon in similarity known as the coinciden ce effect. In coincidence (pronounced ''coincide-ence''), two items th at match on one dimension but have a large difference on another dimen sion receive a higher similarity rating than do two items that have on ly modest differences on both dimensions. We conducted five experiment s in order to examine commonalities between similarity and choice proc esses with respect to coincidence. Four types of tasks were given: sim ilarity ratings, desirability ratings, forced choice similarities (whi ch of two items is most similar to a target), and forced choice prefer ences (which of two items one would prefer, given a target). We found a main effect for ratings as opposed to forced choices, with ratings s howing greater coincidence effects than did choices. Similarity measur es tended to produce more coincidence than did preference measures. Th e overall pattern of results suggests the presence of dimensional weig hting processes sensitive to task characteristics and operating somewh at differently for similarity and decision making.