ORGANIZATIONALBEHAVIORAND HUMAN PERFORMANCE 19, 392--402 (1977) Strategies for the Use of Base-Rate Information JOHN S. CARROLL AND ROBERT S. SIEGLER Carnegie-Mellon University Kahneman and Tversky (PsychologicalReview, 1973, 80, 237-251) found that subjects given both base-rate information about the prevalence of some characteristic within a population and brief personality sketches of individual members of the population base their predictions almost solely on the sketches. Three experiments were done to determine the conditions under which subjects would rely on base-rate information in making predictions about individuals. In Experiment 1 it was found that the combination of a small population, exhaustive sampling of that population, and population percen- tages corresponding to an exact whole number partition of the sample (the "translatability" feature), resulted in substantial reliance on base rates. The results of Experiment 2 suggested that the translatability feature might be especially important in encouraging such usage. However, the results of Ex- periment 3 indicated that the enhanced use of translatable base-rates was limited to situations in which uninformative personality sketches were used. These findings were discussed in terms of Kahneman and Tversky's represen- tativeness construct. Kahneman and Tversky (1973) have uncovered a surprising aspect of the human judgmental process: subjects who are provided both base-rate information about the prevalence of some characteristic within a popula- tion and brief personality sketches of individual members of the popula- tion base their predictions almost solely on the clinical descriptions. The finding holds true even when subjects believe that the clinical descriptions are of little predictive value, when large monetary incentives are provided for correct prediction, and when the base-rate percentages are quite ex- treme. In a different domain, Nisbett and Borgida (1975) demonstrated that base-rate information is ignored in favor of clinical descriptions both in attributions about the causes of past behavior and in predictions of future acts. The evidence for the strength and pervasiveness of the phenomenon is so strong that the question has now become: are human beings ever substantially influenced by base-rate information when clini- cal information is also available? The first purpose of the present study was to answer this question positively--to create a situation in which subjects would rely heavily on base-rate information. The second purpose, assuming that the first goal Requests for reprints should be sent to either author at the Psychology Department, Carnegie--Mellon University, Pittsburgh, Pennsylvania 15213. Order of authorship was ran- domly determined. 392 Copyright'© 1977by Academic Press, Inc. AIIrightsof reproductionin any formreserved. 1SSN 0030-5073