Social stereotypes involve judgments of how typical certain personality traits are of a group. According to the attribution hypothesis, judgments of trait typicality depend on the perceived prevalence of the trait in the target group. According to the categorization hypothesis, such judgments depend on the degree to which a trait is thought to be more or less prevalent in the target group than in a relevant comparison group. A study conducted with women and men as target groups showed that the attribution hypothesis fit the data best when typicality ratings were made in an absolute format. When, however, typicality ratings were made in a comparative format (how typical is the trait of women as compared with men?), both hypotheses received support. Analytical derivation, supported by empirical evidence, showed an inverse relationship between the size of perceived group differences and their weight given in stereotyping. Implications for stereotype measurement and the rationality of social perception are discussed