Outgroup Homogeneity Effect

The phenomenon and classic studies

Quattrone and Jones (1980) showed students the choice of one student from their own or another university and asked them to estimate the choices of that university's students as a whole. People generalized more readily from one student at the other university to the whole group. Park and Rothbart (1982) found that people remember ingroup members in terms of subordinate categories such as occupation or personality, but outgroup members only at the level of the group label. Seeing outgroups as less varied underpins the easy application and maintenance of stereotypes.

Why it happens

Linville and colleagues (1989) proposed a familiarity account, that we know more ingroup members more deeply and therefore perceive more variability, supported by computer simulation. Judd and Park (1988), however, showed that the effect can appear even in minimal groups whose members do not know each other, suggesting familiarity is not enough. From the perspective of social identity theory, categorization that treats the outgroup as a single mass grows stronger as intergroup boundaries become salient. Mullen and Hu's (1989) meta-analysis reported that the effect is small but consistent.

Exceptions and conditions

Simon and Brown (1987) found that members of minority groups may instead show ingroup homogeneity, seeing their own group as more alike, interpreted as emphasizing solidarity when identity is threatened. Ostrom and Sedikides (1992) concluded that the effect is relatively clear in natural groups but mixed in laboratory minimal groups. The effect is used to understand the reduced ability to distinguish other-race faces and discrimination that treats outgroup members as a group rather than as individuals; contact that lets people know outgroup members as individuals can reduce it.

FAQ

What is the outgroup homogeneity effect in simple terms?

The feeling that "people on our side are all different, but people on their side are all alike."

Do people always see outgroups as more alike?

No. Minority groups sometimes see their own group as more alike, and results are mixed for temporary laboratory groups.

Sources reviewed: 2026-10-26

References

1. Quattrone, G. A., & Jones, E. E. (1980). The perception of variability within in-groups and out-groups: Implications for the law of small numbers. Journal of Personality and Social Psychology, 38(1), 141–152. Classic experiment on generalizing from one outgroup member.
2. Park, B., & Rothbart, M. (1982). Perception of out-group homogeneity and levels of social categorization: Memory for the subordinate attributes of in-group and out-group members. Journal of Personality and Social Psychology, 42(6), 1051–1068. Memory for subordinate attributes of ingroup vs outgroup.
3. Judd, C. M., & Park, B. (1988). Out-group homogeneity: Judgments of variability at the individual and group levels. Journal of Personality and Social Psychology, 54(5), 778–788. Tests the effect at individual and group levels.
4. Simon, B., & Brown, R. (1987). Perceived intragroup homogeneity in minority-majority contexts. Journal of Personality and Social Psychology, 53(4), 703–711. Minorities may show ingroup homogeneity instead.
5. Linville, P. W., Fischer, G. W., & Salovey, P. (1989). Perceived distributions of the characteristics of in-group and out-group members: Empirical evidence and a computer simulation. Journal of Personality and Social Psychology, 57(2), 165–188. The familiarity-based exemplar model with simulation.
6. Mullen, B., & Hu, L. (1989). Perceptions of ingroup and outgroup variability: A meta-analytic integration. Basic and Applied Social Psychology, 10(3), 233–252. A meta-analysis of perceived variability.
7. Ostrom, T. M., & Sedikides, C. (1992). Out-group homogeneity effects in natural and minimal groups. Psychological Bulletin, 112(3), 536–552. Reviews natural vs minimal group findings.