What is in-group bias?
In-group bias is the tendency to favour the group one belongs to. Experiments with trivial groups, random groups and five-year-olds show how little it takes, and later research separates favouring one's own from opposing others.
Answer to the question
What is in-group bias?
In-group bias is the tendency to favour members of a group one belongs to over those outside it. Experiments since 1971 have produced it with trivial or random groups, in five-year-olds, in real helping and in cooperation, and research suggests it is mostly extra favour for one's own group, not opposition to others.
Key takeaways
- Tajfel and colleagues (1971) sorted people into groups on a trivial basis; participants favoured their own group when dividing rewards and penalties, and the strongest pull was towards the largest difference in favour of their own.
- Billig and Tajfel (1973) assigned people to random categories and found own-category favouring once the idea of a group was introduced, stronger than when categories were built on similarity.
- Dunham and colleagues (2011) ran three experiments with 140 five-year-olds in randomly assigned groups and found in-group preferences on attitude, resource allocation and expectation measures.
- Levine and colleagues (2005) found an injured stranger in an own-team shirt received more help than one in an unbranded shirt, and a broader shared category extended help to wearers of another club's shirt.
- Balliet and colleagues (2014) pooled studies of cooperation and found a small-to-medium in-group effect (d = 0.32), stronger in social dilemmas (d = 0.42) than in dictator games (d = 0.19); Brewer (1999) argued favouring one's own and opposing others are largely separate.
The study of in-group bias began with a question about size: how little does it take to make a group? Henri Tajfel's team answered in 1971 with a trivial basis for sorting people, and the half century of work since has kept removing reasons for the pattern to exist, one at a time, and finding it anyway.
How Small Can a Group Be?
Participants in the 1971 experiments run by Henri Tajfel's group were sorted into two groups on a trivial basis and then asked to divide rewards and penalties between members of the groups. They gave their own group's members the more favourable shares. The strongest pull was towards the largest possible difference between the two groups in favour of their own, and participants followed it even where doing so meant giving up other gains. Maximising the joint reward regardless of group had no significant effect on how rewards were split, while maximising the own group's reward did. The design became known as the minimal group paradigm.
Michael Billig and Tajfel pushed the idea further in 1973 by assigning people to categories at random, so that nothing real joined the members of either one. Once the idea of a group was introduced, participants favoured their own category, and the favouring was stronger than when categories were built from similarities between individuals. Fairness also pulled on their choices, so the pattern was not a simple grab for advantage.
A minimal group carries no history, no shared fate and no contact. Whatever produced the favouring had to come from the act of being sorted, which is why in-group bias is treated as a different question from its neighbours, each taken up in its own piece: What is group identification, What is entitativity and Why Do We Need to Belong.
| Concept | The question it asks |
|---|---|
| In-group bias | Whether being sorted into a group is enough to tilt a choice towards it |
| Group identification | How far a person takes a group to be part of who they are |
| Entitativity | How far a set of people reads as one thing |
| Need to belong | Why people look for groups at all |
The groups in the children's experiments, published with Yarrow Dunham as first author, were assigned at random, and the 140 five-year-olds had no reason to compete. They showed in-group preferences on explicit and implicit attitude measures, in how they allocated resources, in how they explained behaviour and in what they expected to receive in return. The preferences persisted when the groups were not labelled with a noun, so in-group bias did not depend on a ready-made name.
The children also took in positive information about their own group more readily, and the authors report that this distorted the information they received. A result at age five says when the pattern is already present. It does not say where the pattern came from.
Help on the Street Follows the Shirt a Stranger Wears
Allocation tasks are a long way from daily life, so Mark Levine and colleagues took the question onto the street in 2005. In the first of two field experiments, soccer fans came across an injured stranger wearing either a shirt for the fans' own team or an unbranded sports shirt. The stranger in the own-team shirt received more help. The setting was a real encounter with a real stranger, so the leaning is not confined to laboratory choices about abstract recipients.
Cooperation has been measured far more widely. A meta-analysis published with Daniel Balliet as first author pooled experiments in which people chose whether to cooperate with members of their own group or with outsiders. Across all the comparisons, people cooperated more with their own group, an effect the authors describe as small to medium. The effect was weaker where group members did not depend on each other, as in dictator games, and stronger where they did, as in social dilemmas. It was also stronger when group membership was common knowledge.
The authors concluded that discrimination in cooperation stems more from favouring the in-group than from derogating the out-group, which brings in-group bias back to the minimal studies, where the measured quantity was also a share handed to one's own side.
Is It Favour for Us or Distance from Them?
Marilynn Brewer argued in 1999 that loyalty to a group and negative attitudes towards other groups are largely separate, and that much of what looks like prejudice stems from favouring the in-group rather than from hostility to outsiders. Her paper on in-group bias and prejudice reviews cross-cultural research and laboratory experiments, and it proposes that understanding bias starts with the purposes that forming an in-group serves.
Tribal, a book by Michael Morris, builds a chapter on the same separation and draws on helping studies in which a plain shirt serves as the baseline.
The second of Levine's field experiments varied what the helpers had in mind. A broader shared category was made salient to them, and help then extended to people wearing another club's shirt, though not to people who showed no sign of belonging to any group. In-group bias in these studies tracked the category in the helper's mind, and the minimal studies point the same way, since a trivial or random category was enough to start the pattern.
A category drawn widely enough to take in the wearer of another club's shirt was followed by help for that wearer, while a person with no visible membership of any kind was not helped.
Common questions
What is in-group bias?
In-group bias is the tendency to favour members of a group one belongs to over those outside it. Experiments since 1971 have found it even when groups were formed by random assignment or on a trivial basis.
Does in-group bias mean disliking other groups?
Not necessarily. Brewer argued in 1999 that in-group favouring and hostility to outsiders are largely separate, and a 2014 meta-analysis of cooperation concluded that discrimination there stems more from favouring the in-group than from derogating the out-group.
Does in-group bias need a real group?
No. Studies from 1971 and 1973 produced it with trivial or random categories, and a 2011 set of experiments found it in five-year-olds placed in randomly assigned groups.
Sources
Morris, M. (2024). Tribal: How the Cultural Instincts That Divide Us Can Help Bring Us Together. Seed book; vault hub Books/Tribal.
Tajfel, H., Billig, M. G., Bundy, R. P., & Flament, C. (1971). “Social categorization and intergroup behaviour.” European Journal of Social Psychology, 1(2), 149-178. doi:10.1002/ejsp.2420010202 https://doi.org/10.1002/ejsp.2420010202
Billig, M., & Tajfel, H. (1973). “Social categorization and similarity in intergroup behaviour.” European Journal of Social Psychology, 3(1), 27-52. doi:10.1002/ejsp.2420030103 https://doi.org/10.1002/ejsp.2420030103
Dunham, Y., Baron, A. S., & Carey, S. (2011). “Consequences of ‘minimal’ group affiliations in children.” Child Development, 82(3), 793-811. doi:10.1111/j.1467-8624.2011.01577.x https://doi.org/10.1111/j.1467-8624.2011.01577.x
Levine, M., Prosser, A., Evans, D., & Reicher, S. (2005). “Identity and emergency intervention: How social group membership and inclusiveness of group boundaries shape helping behavior.” Personality and Social Psychology Bulletin, 31(4), 443-453. doi:10.1177/0146167204271651 https://doi.org/10.1177/0146167204271651
Brewer, M. B. (1999). “The psychology of prejudice: Ingroup love and outgroup hate?” Journal of Social Issues, 55(3), 429-444. doi:10.1111/0022-4537.00126 https://doi.org/10.1111/0022-4537.00126
Balliet, D., Wu, J., & De Dreu, C. K. W. (2014). “Ingroup favoritism in cooperation: A meta-analysis.” Psychological Bulletin, 140(6), 1556-1581. doi:10.1037/a0037737 https://doi.org/10.1037/a0037737