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Prisoners Dilemma Introduced

You may well have heard of game theory, and if so, the problem that will spring to mind, indeed perhaps the only one most of us know, is the so-called 'prisoners dilemma'.

There are many variants on the puzzle, however for those not familiar with the dilemma, here is one formulation of it:

Classic Formulation



There are two suspects in a criminal case, A and B. Neither A and B have any contact with each other at all. The police says to A that if A testifies against B, and B remains silent, A goes free whilst B gets a 10 year sentence. If A and B are both silent, both get 6 months in prison. If both A and B speak up, they both get 5 years in prison. B is told exactly the same thing.

So, each prisoner has a clear choice: speak up, or shut up. Speaking up carries with it a risk of getting off or 5 years in jail, shutting up carries a risk of 10 years or 6 months.

The question is: what to do?

Discussing the Dilemma



We assume that both A and B want the shortest possible sentence and they are both 'selfish' in that their sole goal is to get the shortest sentence possible, and helping someone else get off or condeming them to longer in jail does not affect their happiness.

This leads to a situation called a non-zero-sum games, where prisoners co-operate or betray the other.

What is very interesting, then, in this situation is that both will tend to co-operate, even though this doesn't give them the best possible result, i.e. getting off totally free, because they choose to minimise the damage. This is known as being pareto-suboptimal.

There are many real-life applications where the prisoners dilemma and other situations in game theory really do apply. One example is with an arms race between two states. They could both give up weapons or at least reduce them, or increase their powers. Because neither can be sure of what the other is doing (lack of trust) they both increase the weapons they have which is clearly not the optimal solution. The optimal solution is both reducing their number of weapons.

Your Thoughts



What are your thoughts on the prisoners dilemma? Have you come across real-life situations that reflect this in your work or daily life. We would love to hear about them and feature them on this site, so please do let us know.


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