The variability of conditional cooperation in sequential prisoner's dilemmas

We examine how conditional cooperation is related to the material payoffs in a Sequential Prisoner's Dilemma experiment. We have subjects play eight SPDs with varying payoffs, systematically varying the material gain to the second-mover and the material loss to the first-mover when the second-mover defects in response to cooperation. We find that few second-movers are conditionally cooperative in all eight games, and most second-movers change their strategies from game to game. Second-movers are less likely to conditionally cooperate when the gain is higher and when the loss is lower. This pattern is consistent with models of distributional preferences.