Recent work in experimental economics on the effectiveness of rewards and punishments for promoting cooperation mainly examines decentralized incentive systems where all group members can reward and/or punish one another. Many self-organizing groups and societies, however, concentrate the power...

Field evidence suggests that people belonging to the same group often behave similarly, i.e., behavior exhibits social interaction effects. We conduct a laboratory experiment that avoids the identification problem present in the field and allows us to study the behavioral logic of social...