In-group favouritism and social norms: Public goods experiments in Tanzania

The inhabitants of two Tanzanian villages participate in a public goods experiment. Each village consists of multiple sub-villages. Villagers share a social norm of cooperation at the village level. We put emphasis on the sub-village identity in the experiments, and let individuals from the same or from various sub-villages to be matched into a group. In-group favouritism predicts that participants cooperate more when they are in a group from the same sub-village (In-group treatment) than when they are in a group composed of members from different sub-villages (Out-group treatment). We reject this hypothesis. Participants’ expectations of contributions of others do not differ across treatments. However, they respond differently to own expectations across treatments. They contribute on average more than what they expect others to contribute in the Out-group treatment, but less than what they expect others to contribute in the In-group treatment. This is consistent with the activation of the village-level social norm only in the context in which the norm exists, in interactions with other villagers. We emphasise that existing social norms of cooperation need to be considered when making a specific sub-group identity salient with the aim to promote public goods provision.