Prisoner's dilemma

related topics
{theory, work, human}
{game, team, player}
{law, state, case}
{company, market, business}
{rate, high, increase}
{math, number, function}
{war, force, army}
{car, race, vehicle}
{style, bgcolor, rowspan}
{group, member, jewish}

The prisoner's dilemma is a fundamental problem in game theory that demonstrates why two people might not cooperate even if it is in both their best interests to do so. It was originally framed by Merrill Flood and Melvin Dresher working at RAND in 1950. Albert W. Tucker formalized the game with prison sentence payoffs and gave it the "prisoner's dilemma" name (Poundstone, 1992).

A classic example of the prisoner's dilemma (PD) is presented as follows:

If we assume that each player cares only about minimizing his or her own time in jail, then the prisoner's dilemma forms a non-zero-sum game in which two players may each either cooperate with or defect from (betray) the other player. In this game, as in most game theory, the only concern of each individual player (prisoner) is maximizing his or her own payoff, without any concern for the other player's payoff. The unique equilibrium for this game is a Pareto-suboptimal solution, that is, rational choice leads the two players to both play defect, even though each player's individual reward would be greater if they both played cooperatively.

In the classic form of this game, cooperating is strictly dominated by defecting, so that the only possible equilibrium for the game is for all players to defect. No matter what the other player does, one player will always gain a greater payoff by playing defect. Since in any situation playing defect is more beneficial than cooperating, all rational players will play defect, all things being equal.

In the iterated prisoner's dilemma, the game is played repeatedly. Thus each player has an opportunity to punish the other player for previous non-cooperative play. If the number of steps is known by both players in advance, economic theory says that the two players should defect again and again, no matter how many times the game is played. However, this analysis fails to predict the behavior of human players in a real iterated prisoners dilemma situation, and it also fails to predict the optimum algorithm when computer programs play in a tournament. Only when the players play an indefinite or random number of times can cooperation be an equilibrium, technically a subgame perfect equilibrium meaning that both players defecting always remains an equilibrium and there are many other equilibrium outcomes. In this case, the incentive to defect can be overcome by the threat of punishment.

In casual usage, the label "prisoner's dilemma" may be applied to situations not strictly matching the formal criteria of the classic or iterative games, for instance, those in which two entities could gain important benefits from cooperating or suffer from the failure to do so, but find it merely difficult or expensive, not necessarily impossible, to coordinate their activities to achieve cooperation.

Contents

Full article ▸

related documents
Lev Vygotsky
Socratic method
Conceptual metaphor
Judith Butler
Erich Fromm
Northrop Frye
Power (philosophy)
Intellectual capital
Confirmation bias
A New Kind of Science
Game theory
Fortune-telling
Guns, Germs, and Steel
Antonio Gramsci
Averroes
Socionics
Rationalism
Socialist realism
Technological singularity
William James
Where Mathematics Comes From
Fallacy
Cultural studies
Pierre-Joseph Proudhon
Bob Black
John Ruskin
Nobel Prize in Literature
Irony
John Rawls
Fact