[In-group bias in trusting behavior: a choice of allocator experiment with minimal groups]

The purpose of this study is to show that expectations of generalized reciprocity within one's own group are responsible for in-group trust. To test this hypothesis, an allocator choice game in the minimal group situation was used. We assigned the role of a recipient in a dictator game to all 81 subjects, and measured whether they chose to be a recipient of either an in-group or an out-group "allocator" who freely allocate a fixed reward between him/her and a recipient. The results indicate that in-group trust occurs only in the condition in which recipients know that allocators make a reward allocation knowing the group membership of their recipient; recipients show no preference for either an in-group or an out-group allocator when allocators make the decision without knowing the group membership of their recipient. It is thus shown that participants' in-group trust is derived from the general belief that people treat in-group members more favorably than out-group members-a belief about generalized reciprocity within groups.