People often base judgments on stereotypes, even when contradictory base-rate information is provided. In a sample of 438 students from two state universities, we tested several hypotheses regarding why people would prefer stereotype information over base-rates when making judgments: A) People believe stereotype information is more diagnostic than base-rate information, B) people find stereotype information more salient than base-rate information, or C) even though people have some intuitive access to base-rate information, they may need to engage in deliberation before they can make full use of it, and often fail to do so. In line with the deliberative failure account, and counter to the diagnosticity account, we found that inducing deliberation by having people evaluate statements supporting the use of base-rates increased the use of base-rate information. Moreover, counter to the salience and diagnosticity accounts, asking people to evaluate statements supporting the use of stereotypes decreased reliance on stereotype information. Additionally, more numerate subjects were more likely to make use of base-rate information.

Machines are increasingly used to make decisions. We investigated people’sbeliefs about how they do so. In six experiments, participants (totalN = 2664) predicted how computer and human judges woulddecide legal cases on the basis of limited evidence — eitherindividuating information from witness testimony or base-rate information. InExperiments 1 to 4, participants predicted that computer judges would be morelikely than human ones to reach a guilty verdict, regardless of which kind ofevidence was available. Besides asking about punishment, Experiment 5 alsoincluded conditions where the judge had to decide whether to reward suspectedhelpful behavior. Participants again predicted that computer judges would bemore likely than human judges to decide based on the available evidence, butalso predicted that computer judges would be relatively more punitive than humanones. Also, whereas participants predicted the human judge would give moreweight to individuating than base-rate evidence, they expected the computerjudge to be insensitive to the distinction between these kinds of evidence.Finally, Experiment 6 replicated the finding that people expect greatersensitivity to the distinction between individuating and base-rate informationfrom humans than computers, but found that the use of cartoon images, as in thefirst four studies, prevented this effect. Overall, the findings suggest peopleexpect machines to differ from humans in how they weigh different kinds ofinformation when deciding.

Since memory performance expectations may be IQ-based, unidirectional base rate data for IQ-Memory Score discrepancies are provided in the WAIS–III/WMS–III Technical Manual. The utility of these data partially rests on the assumption that discrepancy base rates do not vary across ability levels. FSIQ stratified base rate data generated from the standardization sample, however, demonstrate substantial variability across the IQ spectrum. A superiority of memory score over FSIQ is typical at lower IQ levels, whereas the converse is true at higher IQ levels. These data indicate that the use of IQ–memory score unstratified “simple difference” tables could lead to erroneous conclusions for clients with low or high IQ. IQ stratified standardization base rate data are provided as a complement to the “predicted difference” method detailed in the Technical Manual. (JINS, 2001, 7, 875–880.)