Equilibrium cooperation in two-stage games: Experimental evidence

This paper reports results of an experiment designed to investigate the nature of cooperation and punishment. Subjects are matched in a series of two-person, two-stage games with a sequential equilibrium that supports first-stage cooperation with a credible threat of subsequent punishment. Participants sometimes used a consistent punish/reward strategy, and when they did, cooperation rates increased dramatically. The results thus contradict "payoff relevance": second-stage behavior can be influenced by first-stage outcomes that have no effect on the payoff structure. Nevertheless, high cooperation rates were often not observed, even with a Pareto undominated "punishment" equilibrium in the second stage.