Which is the ideal sanction for cooperation? An experimental study on different types of third-party sanctions.

Cooperation is the crux of many social problems, thus third-party sanction, as one of the most important ways to promote cooperation, is worth studying. The present study compared the effects of third-party punishment alone, third-party reward alone, and the combination of third-party reward and third-party punishment on cooperation in the context of a public goods experiment. In addition, we explored the characteristics of third-party sanctioning behaviors. A total of 280 students participated in the present study. The results showed that the operation of third-party sanctions did raise the level of cooperation and changed the discrete trend of cooperation-specifically, the differences between the cooperation level of every group member and the average level of the whole group. Furthermore, when third-party rewards and third-party punishments were used simultaneously in the public goods game (PGG), the level of cooperation was greatly enhanced, which meant that in the context of the third party, when punishment opportunities and reward opportunities coexist, they may have a "compensatory effect." In terms of the characteristics of sanctioning behaviors, the frequency of third-party sanctions did not differ significantly under different conditions (third-party punishment alone, third-party reward alone, and a combination of third-party reward and third-party punishment), and neither did expenditures on third-party sanctions, but the strategies that third parties used changed under different conditions, thus their effects on other group members' cooperative behavior varied under different conditions. The present study provides a comprehensive picture of how third parties behave in different conditions of third-party sanctions and how these sanctions exert influence on cooperation. Understanding these mechanisms can help us build more effective institutions.