[D_Alex]

> In a single instance of the prisoner’s dilemma, the best strategy is to defect — squeal on your partner and you’ll get less time.

No, that is not right, if it was there would be no dilemma, and this subject would not be discussed ad nauseam. The whole point is that the situation is symmetrical for both players, they should reach the same conclusion and act the same way... and using the strategy of cooperation their outcome is better than defecting.

[crander]

Cooperating is strongly dominated by defecting in Prisoners Dilemma. This is an obvious and very basic game theory result.

Game Theory models strategic situations and doesn't offer insight outside what is modeled. If you think there should be communication supporting cooperation in the game, that game is NOT the Prisoners Dilemma and is in fact another game.

The Prisoners Dilemma is a model that is stacked very much against cooperation. Think about it, the prisoners are held in separate rooms and not allowed to communicate at all in the original story.

[nosuchthing]

Thought experiments are not set in stone, and even if they were modifications could me made.

A real game show [1] put two people in a position of the prisoners dilemma and they were free to communicate. [2]

[1] https://www.youtube.com/watch?v=S0qjK3TWZE8

[2] http://www.radiolab.org/story/golden-rule/

[tjradcliffe]

It gets presented as an obvious and basic game theory result, but it only makes sense if you don't believe in the basic tenants of game theory, amongst which is the claim that it is a theory of maximizing rational actors.

There is no moral choice-making for maximizing rational actors, and both actors in the PD have exactly the same information, including the fact that the other individual is a maximizing rational actor. As such the off diagonal elements of the payoff matrix are irrelevant to any rational decision making because any two rational actors with the same goal will always make the same choice in the same situation. To do anything else would be irrational.

So within the frame of the theory both players know with certainty that because the game is being played by maximizing rational actors that the other player will always do exactly what they do. This is true no matter what they do: the other player will always reach the same conclusion. Rationality dictates it, if rationality means anything at all.

It is only when you smuggle in the possibility of an irrational choice on the part of one of the players that the off-diagonal elements become relevant, because one player can for unaccountable reasons choose to do something irrational, which a maximizing rational actor would never do.

Game theory is not about people. It's about rational actors who want to maximize their payoff. For such entities there is no dilemma, since only the diagonal elements of the matrix matter, and cooperation is the obvious maximizing strategy.

Unfortunately, game theory under this constraint becomes very boring. There is probably a salvagable variant of it that remains interesting, but I'm honestly not sure what it's a theory of. "Semi-rational not-very-smart actors"? That would describe humans reasonably well, I guess. It certainly describes me. Or maybe the decision-maker being analyzed could be considered a rational actor and the rest of the players irrational, although that would be equivalent to playing against a random number generator.

[yarrel]

Iterated Prisoners dilemma is less clearly stacked in favour of defecting, although I assume that the actors' memories would fall under "communication":

http://en.wikipedia.org/wiki/Prisoner%27s_dilemma#The_iterat...

[crander]

Yes, a repeated game like Iterated PD is a different game with a different solution. The Grim strategy for example.

[vacri]

I always found it interesting that the Prisoner's Dilemma is so context-free. For a lot of criminals, doing a moderate amount of jail time is far preferable to being a snitch. No point in getting out early if you're facing vicious repercussion from your peers.

[sukilot]

"domination" is a local phenomenon PD shows that local phenomena do not generalize to global solutions.

http://en.m.wikipedia.org/wiki/Superrationality

[Retra]

I would give this a read:

http://lesswrong.com/lw/tn/the_true_prisoners_dilemma/

[MBlume]

If I duplicated you and made you play a PD against your duplicate and then sent you off to different corners of the universe to enjoy the spoils, would you cooperate or defect?

[DennisP]

Yes but the dilemma is that no matter what the other person does, you are better off by defecting. You get a good outcome if you both cooperate. If he defects, you get a horrible outcome if you cooperate. If he cooperates, you get a decent outcome by cooperating, but an even better outcome by defecting.

Since both players think this way, they both defect and get a bad outcome.

Real prisoners don't always defect, but the reason is that they're not actually playing the prisoner's dilemma. The payoff matrix has been altered....eg., by severe penalties for ratting, which give the player a much worse outcome for defecting. Those penalties wouldn't be necessary if the dilemma weren't real. (Another alteration would be if the prisoners care enough about each other so each sees it as a bad outcome if the other suffers. This isn't contrary to game theory, it's just a different set of payoffs.)

[Retric]

Depending on the risks a somewhat random strategy can work out really well. IE if both defect they both get 10 years if none defect both get 9 years, and if one defects the other gets 15 years. Now if they both defect 10% of the time the 19% of the time there better off collectively as 9+9 > 15 saving 3 years and 1% of the time there worse off by 2 years collectively.