Heterogeneity in the Motivations for Punishment: An Experimental Study

We explores the motivations behind costly punishment in social dilemmas, specifically focusing on reciprocity and inequality aversion. To distinguish these motivations, we introduce uncertainty into the payoff function of a public goods game, preventing participants from predicting others' contributions based on their payoffs. In this situation, participants should choose between others' contributions and others' payoffs as the criterion for their punishment. We also include a random income game to test the plausibility of our classification by removing intentionality from the contribution decisions. Our results show heterogeneity in the motivations to punish, leading to different types of punishers: the self-interested type, the reciprocal type, the inequality-averse type, and the ``other" type who is inconsistent. Furthermore, in the random income game, overall punishment tends to be lower, but only reciprocal punishment decreases with the existence of intention. Additionally, the reciprocal type strongly punishes free-riding behaviors but also imposes some punishment for payoff inequality. These findings reveal that inequality aversion is a critical motivation for punishment---that is, that a significant number of individuals rely on inequality aversion as their sole motivation for punishment while others incorporate it into their punishment based on reciprocity.

本研究探讨了社会困境（social dilemmas）中的代价性惩罚（costly punishment）动机，重点聚焦于互惠（reciprocity）与规避不平等（inequality aversion）两大核心动因。为区分这两类动机，我们在公共品博弈（public goods game）的收益函数中引入不确定性，使得参与者无法依据自身收益推断他人的贡献水平。在此情境下，参与者需以他人贡献或他人收益作为惩罚的评判标准。此外，我们设置了随机收益博弈（random income game），通过剥离贡献决策中的意图性来验证我们的动机分类是否合理。

研究结果显示，惩罚动机存在显著异质性，据此可将惩罚者划分为四类：自利型、互惠型、规避不平等型，以及行为不一致的“其他型”。进一步分析表明，在随机收益博弈中，整体惩罚水平普遍偏低，但仅互惠型惩罚会因贡献决策缺乏意图而出现显著下降。同时，互惠型惩罚者不仅会严厉惩罚搭便车（free-riding）行为，还会因收益不平等实施一定程度的惩罚。

上述研究结果揭示，规避不平等是惩罚行为的关键动机：相当一部分个体仅以规避不平等作为惩罚的唯一动机，而另一部分个体则将其与互惠动机结合，以此实施惩罚行为。