structural:scholar_edition, information:highlighting, linguistic:translation, stylistic:tone
Illusory correlation

Research has shown that stereotypes can develop based on a cognitive mechanism known as illusory correlation – an erroneous inference about the relationship between two events. If two statistically infrequent events co-occur, observers overestimate the frequency of co-occurrence of these events. The underlying reason is that rare, infrequent events are distinctive and salient and, when paired, become even more so. The heightened salience results in more attention and more effective encoding, which strengthens the belief that the events are correlated.

In the inter-group context, illusory correlations lead people to misattribute rare behaviors or traits at higher rates to minority group members than to majority groups, even when both display the same proportion of the behaviors or traits. Black people, for instance, are a minority group in the United States and interaction with blacks is a relatively infrequent event for an average white American. Similarly, undesirable behavior (e.g. crime) is statistically less frequent than desirable behavior. Since both events "blackness" and "undesirable behavior" are distinctive in the sense that they are infrequent, the combination of the two leads observers to overestimate the rate of co-occurrence. Similarly, in workplaces where women are underrepresented and negative behaviors such as errors occur less frequently than positive behaviors, women become more strongly associated with mistakes than men.

In a landmark study, David Hamilton and Richard Gifford (1976) examined the role of illusory correlation in stereotype formation. Subjects were instructed to read descriptions of behaviors performed by members of groups A and B. Negative behaviors outnumbered positive actions and group B was smaller than group A, making negative behaviors and membership in group B relatively infrequent and distinctive. Participants were then asked who had performed a set of actions: a person of group A or group B. Results showed that subjects overestimated the frequency with which both distinctive events, membership in group B and negative behavior, co-occurred, and evaluated group B more negatively. This despite the fact the proportion of positive to negative behaviors was equivalent for both groups and that there was no actual correlation between group membership and behaviors. Although Hamilton and Gifford found a similar effect for positive behaviors as the infrequent events, a meta-analytic review of studies showed that illusory correlation effects are stronger when the infrequent, distinctive information is negative.

Hamilton and Gifford's distinctiveness-based explanation of stereotype formation was subsequently extended. A 1994 study by McConnell, Sherman, and Hamilton found that people formed stereotypes based on information that was not distinctive at the time of presentation, but was considered distinctive at the time of judgement. Once a person judges non-distinctive information in memory to be distinctive, that information is re-encoded and re-represented as if it had been distinctive when it was first processed.