Overconfidence in case-study judgments.

It is a common phenomenon of clinical practice that as a psychologist accumulates casestudy material about another human being, he comes to think that he knows that person pretty well. Consequently, sooner or later in the information-gathering process, the psychologist becomes confident enough to make diagnostic conclusions, describe the client's main dynamics, and perhaps even venture to predict his future behavior. Though the psychologist's conclusions may remain tentative, his increase in confidence from the time of first approaching the case to the time of writing his report is usually very marked. This study investigated whether that increase in confidence is justified by a corresponding increase in accuracy of conclusions. Though the psychologist's confidence in his conclusions has often been mentioned as an important subject of scientific inquiry (Meehl, 1957), it has only rarely been studied intensively. Furthermore, when it has been studied, rather surprising findings have often resulted. For instance, Goldberg (1959) and Oskamp (1962) have shown that the diagnostic confidence of experienced psychologists is less than that of less experienced persons. The same studies and many others have also shown that professional psychologists are no better interpersonal judges, and sometimes are worse 1 Revision of a paper presented at the Western Psychological Association annual meeting, April 18, 1964. Thanks are due to Stanley Lunde for his help in constructing the case-study test. ones, than are untrained individuals (Taft, 1955).