In-Group and Out-Group Bias

What it is

The term covers a family of findings in which people treat members of their own group more favourably than members of other groups. The favouring has been measured in how rewards are divided, in attitudes, in what children expect to receive in return, in whether people cooperate and in whether a bystander stops to help.

The foundation is the minimal group research. Participants in the 1971 experiments run by Henri Tajfel's group were sorted into groups on a trivial basis and divided rewards and penalties between members of the groups. They favoured their own group, most strongly towards the largest difference in favour of it. Michael Billig and Tajfel assigned people to random categories in 1973 and found own-category favouring once the idea of a group was introduced, stronger than when categories were built from similarities between individuals. These designs are described on the page for the minimal group paradigm.

Three experiments published in 2011 with Yarrow Dunham as first author placed 140 five-year-olds in randomly assigned groups. The children showed in-group preferences across explicit and implicit attitude measures, resource allocation, behavioural attribution and expectations of reciprocity, and they preferentially encoded positive information about their own group.

The strength of the effect varies with the setting. A meta-analysis published with Daniel Balliet as first author pooled experiments on cooperation and reported a small-to-medium in-group effect (d = 0.32). It was weaker where group members did not depend on each other, as in dictator games (d = 0.19), and stronger in social dilemmas, where they did (d = 0.42). It was also stronger when group membership was common knowledge.

In effect

In research: favouring without opposing

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. The 2014 meta-analysis reached a related conclusion about cooperation: discrimination there stems more from favouring the in-group than from derogating the out-group. Michael Morris draws the same separation in his book Tribal.

In the street: help from a stranger

In the first of two field experiments reported by Mark Levine and colleagues in 2005, soccer fans came across an injured stranger wearing either an own-team shirt or an unbranded sports shirt. The stranger in the own-team shirt received more help. The second experiment made a broader shared category salient to the helpers, and help extended to people wearing another club's shirt but not to people who showed no sign of belonging to any group.

In the design of groups: where the boundary is drawn

The helping result suggests the boundary that matters is the one the helper has in mind. A category drawn widely enough to include a stranger was followed by help for that stranger. Teams, communities and services that want goodwill to reach beyond a core group can read the result as a reason to describe the shared category broadly. That is an interpretation of one pair of field studies, not a tested programme.

What it does not say

In-group bias does not mean hostility to other groups, and the research cited here points the other way: the best-supported claim is that people extend extra favour to their own. It does not show that the favouring is large in every setting, since the cooperation effect was small to medium and varied by setting. It does not show that the pattern is innate, since a result in five-year-olds says when it is present, not where it came from. And the minimal group experiments show what a bare label can do when it is the only information available; they do not show that labels alone account for favouring among people who share a history.

Who developed it

The experimental tradition begins with Henri Tajfel and colleagues in 1971, extended by Michael Billig. Later work includes Yarrow Dunham on children, Mark Levine on helping, Marilynn Brewer on favouring versus hostility, and Daniel Balliet on cooperation.

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