Prisoner's Dilemma

Prisoner's Dilemma A paradigmatic instance in game theory, which takes its name from a story of two prisoners, who are interrogated separately and cannot communicate with each other. There is insufficient evidence for the police to convict either prisoner of armed robbery, so that unless they confess, each will receive a relatively light sentence of one year's imprisonment for illegal possession of firearms. The prosecuting authorities offer each prisoner a deal, whereby they may confess and turn state's witness against the other prisoner (putting him away for ten years), while they themselves will be set free. The catch is that, if both prisoners confess, each will be convicted of armed robbery and sent to jail for six years. The dilemma facing the individual prisoner is whether or not to confess. The self-interested prisoner is better off confessing, no matter what his partner does, since if both prisoners see the issue in this way they will each spend a maximum of six years in jail. If, on the other hand, each could be sure that the other would act in the group interest (rather than pursuing self-interest), both would hold out, and each spend only a year in jail. The worst possible outcome would be to act in pursuit of the group interest while one's partner acted self-interestedly—since ten years in jail would be the result. The case of the Prisoner's Dilemma is commonly used to illustrate the dangers of committing the fallacy of composition and to explore the conditions of collective action. See also ALTRUISM.