Multiple prisoner's dilemma games with (out) an outside option: An experimental study

Experiments in which subjects play simultaneously several finite prisoner's dilemma supergames with and without an outside option reveal that: (i) subjects use probabilistic start and endeffect behaviour, (ii) the freedom to choose whether to play the prisoner's dilemma game enhances cooperation, (iii) if the payoff for simultaneous defection is negative, subjects' tendency to avoid losses leads them to cooperate; while this tendency makes them stick to mutual defection if its payoff is positive.