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.