An experimental test of a game-theoretical model of reciprocity

In this contribution the norm of reciprocity is defined as a basic internal motivation. Using formal tools of game theory, a model of social utility function is presented. The reciprocity model predicts that social actors should reciprocate costs and benefits they receive, even when there are costs in conforming to the norm. Hypotheses about actors’ behavior, expectations and evaluations are derived from the model. The hypotheses were tested in an experimental situation, the reciprocity game, consisting of a prisoner’s dilemma game (PD) followed by a dictator game (DG). The sample was composed of 74 Italian undergraduate students. In line with the model’s predictions, the experimental results showed that participants reciprocate the behavior of the opponent in the PD. In the DG, if the opponent cooperated, participants gave back an almost equal share, whereas if the opponent defected, participants gave a minimal amount. These reciprocity effects are modulated by individual differences in the concern for reciprocity.