Monetary and Nonmonetary Punishment in the Voluntary Contributions Mechanism
研究自愿贡献机制中货币惩罚（罚款）与非货币惩罚（同伴压力、社会排斥）对合作行为的影响，比较两种制裁方式的效力。
A demand for behavioral norms arises when members of a group have individual incentives to take actions that reduce the group’s overall welfare (James S. Coleman, 1990). Norms require enforcement with a system of sanctions that penalize deviations from acceptable behavior (George C. Homans, 1961). Formal sanctions include fines or restrictions implemented by a legal system or private individuals that impose costs of money and time on the offender. However, informal sanctions such as peer pressure, gossip, or social ostracism might in some cases also be effective deterrents, and expressions of social acceptance might be effective in encouraging group-oriented behavior (Peter M. Blau, 1964). Indeed, the fact that expressions of approval and disapproval are commonly observed in human interaction suggests that they must influence the behavior of at least some individuals. In recognition of the importance of informal sanctions, economists have integrated phenomena such as peer pressure