In a series of studies, subjects were asked to make predictions about target individuals. Some subjects were given information about the target which pretest subjects had judged to be "diagnostic''-that is, had judged to be usefully predictive of the outcome. Other subjects were given a mix of information judged to be diagnostic and information judged to be "nondiagnostic" by pretest subjectsthat is, judged to be of little value for predicting the outcome. Subjects given mixed information made much less extreme predictions than did subjects given only diagnostic information. It was argued that this "dilution effect" occurs because people make predictions by making simple similarity judgments. That is, they compare the information they have about the target with their conception of outcome categories. The presence of individuating but nondiagnostic information about the target reduces the similarity between the target and those outcomes that are suggested by the diagnostic information. One of the major implications is that stereotypes and other "social knowledge structures" may be applied primarily to abstract, undifferentiated individuals and groups and may be largely set aside when judgments are made about concrete, individuated people.

I have often noticed that we are inclined to endow our Social judgment often utilizes only a fracfriends with the stability of type that literary characters tion of the ava ii able information. The voter rr^ZtS'tv^r STJSSZ god who examines a candidate, the clinician who king banging his tankard in high revelry, all woes for-diagnoses the cause Of some trouble, and the gotten, at a jolly reunion, with all three daughters and admissions officer who assesses a Student's their lapdogs ... we expect our friends to follow this pro spects of SUCC6SS must all select the inor that logical and conventional pattern we have fixed formation the cons i der to be relevant or for them . . . any deviation in the fates we have or-. . 3. . darned would strike us as not only anomalous but uneth-diagnostic for their judgments. Often, they ical. We would prefer not to have known at all our neigh-must extract the diagnostic information from bour, the retired hot-dog stand operator, if it turns out a broad data base that also contains other he has just produced the greatest book of poetry his age m f orrnat ion that is nondiagnostie, or devoid has seen.-V L ADiM. R NABOKOV.Qf aQy predictive yalue for that specific j udg .. ment. This report is based on a PhD dissertation at the Uni-Current research has been mainly conversity of Michigan. The research was supported in part cerned with describing the Strategies people by Grant BNS 75-23191 from the National Science use for p roces sin g complex diagnostic infer-Foundation to Richard E. Nisbett. I am especially

This study examined the certainty with which children make their judgments on concrete-operational tasks. The subjects were 60 second graders and 36 fifth graders; the tasks involved various forms of conservation and transitivity. Three methods of assessing certainty were included: a rating scale, a betting game, and a feedback phase in which the child responded to a disconfirmation of his answer. Children who had given operational answers expressed strong certainty in their judgments on both the rating and betting measures. The certainty expressed during the feedback phase, as measured by challenges to the disconfirmation, was considerably less. Operational answers were accompanied by greater certainty than were nonoperational answers. Developmental changes in certainty among operational subjects were infrequent, as were interconcept differences in certainty. There was evidence, however, that conservation of number was the concept held with greatest certainty. The results are discussed in terms of Piaget's claim that concepts of conservation and transitivity are experienced as logically necessary truths.

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