Reduce hostility between groups by having them work together, as equals, toward a goal that both want and neither can reach alone; mere exposure or exhortation does little, but cooperative contact under the right conditions reliably lowers prejudice.

How to do it

1. 1Find a goal that is real and shared: the flooded road, the school budget, the league that needs enough players, the deadline both departments will miss. It must matter to both groups and require both.
2. 2Set the conditions Allport identified: equal status within the activity, cooperation and not competition between the groups, and visible support from authorities or norms both sides respect.
3. 3Mix the teams. Do not pit one group against the other, even in fun; structure tasks so that success depends on people from both groups.
4. 4Make it repeated and long enough for acquaintance. One event produces a pleasant afternoon; a season produces friendships.
5. 5Let people be individuals. Arrange work in pairs or small groups where personal information is naturally exchanged, while group identities remain visible enough that goodwill generalizes beyond "the exception".
6. 6Arrange an early, achievable success, and expect friction. In the original study, several joint tasks were needed before hostility dropped.
7. 7As an individual, join something cross-cutting (a sports team, a volunteer crew, a choir, a mutual-aid group) where the people you have been told to fear are simply teammates.

When to use it

• •A workplace, school, congregation, or neighbourhood divided into hostile camps.
• •After a merger, a redistricting, or an influx of newcomers.
• •When outside actors are profiting from setting two local groups against each other.
• •Designing youth, sport, or community programmes meant to build cohesion.

Counters

Evidence and how strong it is

Sherif et al. (1961) reported that at the Robbers Cave camp two groups of boys, made hostile through competition, were not reconciled by pleasant shared activities but became friendlier after a series of problems (a failed water supply, a stalled truck) that required joint effort. Allport (1954) specified the conditions under which contact reduces prejudice. Pettigrew & Tropp (2006) meta-analysed 515 studies and found that intergroup contact typically reduces prejudice (average correlation around -0.21), more strongly when Allport's conditions are met, and that the effect generalizes beyond the individuals met. Evidence strength: good overall, with important qualifications. Perry (2018), using archival records, shows that the Robbers Cave study was heavily stage-managed and that an earlier attempt in which the boys did not turn on each other went unpublished, so it is an illustration and not proof. Paluck, Green & Green (2019) restricted the contact literature to randomized experiments with delayed outcomes and found positive but smaller and more variable effects, with little evidence for adults and for ethnic or racial prejudice specifically. A randomized field experiment by Mousa (2020), mixing Christian and Muslim players on soccer teams in post-ISIS Iraq, improved behaviour toward teammates of the other group but did not generalize to the wider outgroup.

1. Sherif, M., Harvey, O. J., White, B. J., Hood, W. R., & Sherif, C. W. (1961). Intergroup Conflict and Cooperation: The Robbers Cave Experiment. University of Oklahoma Book Exchange
   The original report that superordinate goals, not mere pleasant contact, reduced hostility between the two groups.
2. Allport, G. W. (1954). The Nature of Prejudice. Addison-Wesley
   The statement of the contact hypothesis and its optimal conditions: equal status, common goals, cooperation, and institutional support.
3. Pettigrew, T. F., & Tropp, L. R. (2006). A Meta-Analytic Test of Intergroup Contact Theory. Journal of Personality and Social Psychology, 90(5), 751-783
   Meta-analysis of 515 studies finding that contact reduces prejudice, most strongly under Allport's conditions.
4. Paluck, E. L., Green, S. A., & Green, D. P. (2019). The Contact Hypothesis Re-Evaluated. Behavioural Public Policy, 3(2), 129-158
   Review restricted to randomized studies showing smaller, more variable effects and gaps in the evidence for adults.
5. Perry, G. (2018). The Lost Boys: Inside Muzafer Sherif's Robbers Cave Experiment. Scribe
   Archival critique showing the extent of experimenter intervention and an earlier unpublished failed attempt.
6. Mousa, S. (2020). Building Social Cohesion Between Christians and Muslims Through Soccer in Post-ISIS Iraq. Science, 369(6505), 866-870
   Randomized field experiment showing cooperative contact improved behaviour toward teammates without generalizing to the wider outgroup.