Time to Defect: Repeated Prisoners’ DilemmaExperiments with Uncertain Horizon

Using a symmetric 2-person prisoners’ dilemma as the base game, each playerreceives a signal for the number of rounds to be played with the same partner.The actual number of rounds (the length of the supergame) is determined bythe maximal signal where each player expects the other’s signal to be smaller,respectively larger, by a fixed number of rounds with 50% probability. In thetradition of Folk Theorems we show that both, mutual defection and mutualcooperation until the individually perceived last round, are subgame perfectequilibrium outcomes. We find experimental evidence that many players do infact cooperate beyond their individual signal period.