The iterated prisoner's dilemma is just like the regular game except you play it multiple times with an opponent and add up the scores. But it can change the strategy and has more real world applications as it resembles a relationship.
THE PRISONER'S DILEMMA • The Prisoner's Dilemma
FOOT NOTES
Additional requirements for an iterated prisoner’s dilemma game
For a one off prisoner’s dilemma, they payoffs can just be like 5 greater than 3 greater than 1 greater than 0 (like in the video). But for an iterated prisoner’s dilemma game to be an iterated prisoner’s dilemma game, the total payout for both cooperating has to be bigger than the total payout for one person cooperating and one person defecting. Basically 2x3 greater than 5+0.
If it was like 8 points for defecting while the other cooperates, it would still follow the on off prisoners dilemma format, 8 greater than 3 greater than 1 greater than 0. But with an iterated prisoner’s dilemma game the best strategy would be to go back and forth between cooperating and defecting (giving them on average 4 each, rather than 3 for both cooperating). Which can happen for sure, but it’s a different sort of game.
With a one-off prisoner’s dilemma this doesn’t matter so much. Trade might change the relationship, but it should still appear as a prisoner’s dilemma. The incentives that make it the prisoner’s dilemma would be the same. Their best strategies would still be to always defect.
Tournament 1 vs tournament 2 (A set number of rounds vs not knowing when it ends)
There is a bit of a logical quirk when the players know how many rounds there are. A big part of game theory is getting into your opponents head, predicting what they will do. Also thinking about the whole game and reasoning backwards.
So when they know how many rounds there are, the last round against any given opponent, has no consequences. If you defect in the first round the opponent can reciprocate and you probably won’t be better off or it. But an opponent can’t reciprocate against any defecting in that last round. And since no matter what the other person is going to do, defecting gives a better payout. A player should defect in the last round... so should everyone really. They will only get more for doing that. We should expect them to do it.
But then if everyone is defecting in the last round, not in response to anything that happened before, then really the second to last round also has no consequences. Nobody is going to defect because you defected in the second to last round. What they’re doing in that next round is already set, if we defect in the second to last round we’re not giving up future gains we could have gotten while cooperating. So everyone should defect in the second to last round because there are no consequences and the payoff is higher. But then if everyone is defecting in these rounds, then the third to last round also has no consequences…. Blah blah, defect the whole time. With this reasoning the correct strategy is to always defect.
But we already know that ALWAYS DEFECT isn’t a great strategy here. Because defecting has consequences.
But reasoning backwards, in this context, only works if everyone is doing it. If everyone has thought that way. If everyone reasoned this way, then everyone is always defecting. Then always defecting is the best strategy against that.
But the people who submitted for this tournament clearly didn’t reason this way.
Maybe because most of the time in the real world, we don’t know how many rounds there are, so we always think our actions will have consequences. Also we rarely interact with one person in isolation. We can build a reputation for being un-cooperative. If we are dicks to people who we are about to never see again those who will may not want to cooperate with us as much. So those who submitted thought like this.
Maybe because they didn’t know about the idea.
But even still, in the context of that tournament it would still better to defect in the last round. I suspect TIT FOR TAT or FORGIVING TIT FOR TAT modified to defect in the last round would have won... in the tournaments at least. If you're done with a relationship and you kill them and take your stuff, the people watching you won'y want to cooperate with you.
For that tournament they actually changed the definition of what a “nice” strategy was to allow defecting in those last few rounds against an opponent. The weird space where the two ideas meet.
Cooperating with whom?
Cooperation and defection refer to between the two players. Not necessarily with outside forces like with the police.
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