Deterrence or Punishment? How Punishment Schemes Affects Cooperative Behavior

Punishment serves as a critical governance tool for curbing free-riding in public goods provision, but its efficacy depends on the combined effects of detection probability and punishment severity. Most existing studies have examined these two dimensions in isolation, and few have distinguished between the ex ante deterrent effect and the ex post punitive effect. This study employs a repeated public goods experiment, consisting of a no-punishment baseline and three treatment groups with identical expected punishment but different schemes: low detection probability with high fines, medium detection probability with medium fines, and high detection probability with low fines. We examine how punishment schemes affect individual cooperative behavior. The results show that all three punishment designs significantly increase cooperation. Under fixed expected punishment, heterogeneous governance effects emerge across different probability-severity combinations; the medium-probability and medium-severity scheme generates the strongest cooperative incentives. Moreover, punishment promotes cooperation primarily through ex ante deterrence rather than ex post actual punishment. These findings depart from the predictions of traditional expected value theory and provide experimental evidence for understanding the differentiated governance effects of alternative punishment schemes.