Individual strategy choice in the repeated Prisoner’s Dilemma
通过重复囚徒困境实验，识别出三种行为类型：背叛者、谨慎合作者和强合作者，发现合作主要由少数稳健行为模式维持，且合作者的持续行为对预期收益不敏感。
Repeated interactions can sustain cooperation even when short-run incentives favor defection, but the individual strategies underlying such cooperation remain poorly understood. We study behavior in indefinitely repeated Prisoner’s Dilemma experiments and identify three robust behavioral types: defectors defectors, cautious cooperators, and strong cooperators. Both types of cooperators tend to continue cooperation after mutual cooperation, defect after mutual defection, and randomize after asymmetric outcomes, differing mainly in their initial willingness to cooperate. Variation in the strategic environment primarily changes the population shares of these types rather than their continuation behavior. These findings suggest that cooperation in repeated interactions is sustained by a small number of robust behavioral patterns. At the same time, the continuation behavior of cooperating types is largely insensitive to expected payoffs, contrary to standard game-theoretic predictions.