Faculty Scholarly Dissemination Grants


When belief bias attenuation leads to poorer judgments: Debiasing judgments on an ecologically valid task




College of Liberal Arts and Sciences

Date Range



A well established finding in the research on judgment and reasoning is that people are overly influenced by prior beliefs. The current research addresses the normative status of the so-called belief bias effect. Participants were asked to judge the height of several males and females individually presented in 116 photographs. Overall, the height of the males tend to be overestimated and the height of the females tend to be underestimated. In short, participants are overly influenced by a true prior belief (viz., males are on average taller than females). These systematic over- and underestimations with target sex represents an example of belief bias. It remains an open question whether debiasing judgments will result in more, less or no change in judgment accuracy. A total of 132 participants were given a pretest and post test version of the height judgment task. There were no indications that belief bias resulted in a deleterious effect on judgment accuracy when an ecologically valid task was used. In fact, belief bias on the pretest facilitated judgment accuracy. The post test results demonstrated that participants who were in the debiased condition incurred the extra cost of time spent on the task without any accompanying benefits. Indeed the successful debiasing manipulation resulted in less accuracy in one crucial measure of actual judgment performance.

Conference Name

72nd Annual Convention of the Canadian Psychological Association

Conference Location

Toronto, ON Canada

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