Endogenous Group Formation via Unproductive Costs
实验发现，自愿加入降低私人投资回报率的群体能筛选出搭便车者，吸引条件合作者，从而提升群体产出和成员福利，这种牺牲机制在监督困难时尤为有效。
Sacrifice is widely believed to enhance cooperation in churches, communes, gangs, clans, military units, and many other groups. We find that sacrifice can also work in the lab, apart from special ideologies, identities, or interactions. Our subjects play a modified VCM game-one in which they can voluntarily join groups that provide <i>reduced</i> rates of return on private investment. This leads to both endogenous sorting (because free-riders tend to reject the reduced-rate option) and substitution (because reduced private productivity favours increased club involvement). Seemingly unproductive costs thus serve to screen out free-riders, attract conditional cooperators, boost club production, and increase member welfare. The sacrifice mechanism is simple and particularly useful where monitoring difficulties impede punishment, exclusion, fees, and other more standard solutions.