Population base rates as anchors in social categorization under uncertainty1

Abstract

People often underutilize the numerical minority group when determining category membership of individuals into perceptually ambiguous social categories (i.e., groups whose members are relatively difficult to accurately identify based on visual information). We find that perceived population base rates can underlie this bias and influence social categorization even when stimulus set base rates are equated. We also provide evidence for an anchoring account to explain this bias. In Experiments 1 and 2, lower experimenter-provided population base rates of the minority group led to reduced utilization of the minority group, while higher base rates increased utilization. In Experiment 3, self-generated population base rates produced the same result and mediated the effect of anchors on categorization. An additional study suggests that anchoring on population base rates is unintentional, and that people insufficiently adjust toward stimulus set base rates. These findings highlight the importance of population base rates in categorizing members of perceptually ambiguous social groups.