December 15, 1965
University of Michigan Press
The term “Prisoner’s Dilemma” comes from the original anecdote used to illustrate this game of strategy. Two prisoners, held incommunicado, are charged with the same crime. They can be convicted only if either confesses. If both prisoners confess, their payoff is minus one. If neither confesses it is plus one. If only one confesses he is set free for having turned state’s evidence and is given a reward of plus two to boot. The prisoner who holds out is convicted on the strength of the other’s testimony and is given a more severe sentence than if he had confessed. His payoff is minus two. It is in the interest of each to confess no matter what the other does but it is in their collective interests to hold out.
There is no satisfactory solution to the paradox of this game. Its simplicity is misleading, and attempts to analyse it carry you deeper and deeper into the maze of intricate and interrelated questions which it is impossible to keep on a purely “rational” level. What seems rational from your own point of view, turns out to be detrimental in the end.
This book is an account of many experiments in which Prisoner’s Dilemma was played. Sometimes the players did one thing, and sometimes another. Still, when all the data were analysed, definite patterns of behavior emerged. Whether the players cooperated and to what degree depended on the stakes involved, on what they learned from their experience, on their sex, and on whether they played against the same or opposite sex.
We learn how people are motivated to trust or distrust their partners, to keep faith or to betray, to be guided by joint or selfish interest. The method represents an important step toward building a bridge between scientific psychology and interesting psychology.
Anatol Rapoport is Professor of mathematical biology and senior research mathematician, Mental Health Research Institute, the University of Michigan. He is the author of Science and the Goals of Man, Operational Philosophy, Strategy and Conscience, and Fights, Games, and Debates.
Albert M. Chammah is an assistant research communication scientist at The University of Michigan’s Mental Health Research Institute. Mr. Chammah has published articles in Behavioral Science and the Journal of Abnormal and Social Psychology.