How intergroup relation moderates group bias in Third-Party Punishment

Two experiments were conducted to investigate how intergroup relation moderates group bias in Third-Party Punishment (TPP) of selfishness. Participants competed or cooperated with the other group and then performed a TPP task in which they could reduce an allocator's benefits after paying a low cost (paying 1/3 unit deducts 1 unit of the allocator in Experiment 1, n = 76) or a high cost (paying 1 unit deducts 1 unit of the allocator in Experiment 2, n = 81). The results supported the "mere-preference hypothesis" of group bias, showing that people were more likely to tolerate their ingroups while punishing outgroups more harshly. Furthermore, when the cost was low, competition increased people's punishment toward outgroups' selfishness but not toward ingroup members, thus enlarging the group bias. When the cost was high, however, this effect disappeared, indicating that people consider a "cost-to-impact ratio" when selectively enforcing the fairness norm in intergroup conflicts. Our findings suggest how intergroup relation and cost-benefit analysis interact together to influence the group bias in TPP, providing insights into mechanisms underlying the maintenance of fairness norms and decision-making in a group context.