Factors affecting co‐operation in the prisoner's dilemma

Two suspects are taken into custody and separated. The district attorney is certain that they are guilty of a specific crime, but he does not have adequate evidence to convict them at a trial. He points out to each prisoner that each has two alternatives: to confess to the crime the police are sure they have done, or not to confess. If they both do not confess, then the district attorney states he will book them on some very minor trumped‐up charge such as petty larceny and illegal possession of a weapon, and they will both receive minor punishment; if they both confess they will be prosecuted, but he will recommend less than the most severe sentence; but if one confesses and the other does not, then the confessor will receive lenient treatment for turning state's evidence whereas the latter will get the book slapped at him. (Luce & Raiffa, 1957, p. 95). The “Prisoner's Dilemma”—to co‐operate or to defect, to trust or to distrust, to sacrifice immediate profit for the sake of long‐run gain—is a situation which occurs time and again in the marketplace, in the smoke‐filled rooms of a political convention, on Wall Street, and on Capitol Hill. Games of strategy have been devised for experimental study of this dilemma. But “pure” game theory assumes completely rational players, and as every reader will attest, human beings can be anything but rational. Often players will base their strategies on factors other than the rules of the game. This paper describes an investigation of three of these factors which may affect co‐operation in Prisoner's Dilemma games.