Too few British people act cooperatively to solve a variation of the famous game theory puzzle – and Tories and Londoners are especially uncooperative

A psychology professor's extra credit question for students at the University of Maryland drew significant media interest last week, as the public grappled with a solution to the puzzle. The question, a variation of the famous prisoner's dilemma, asks respondents to choose between having two or six points added to their final grade, but there's a catch – if more than 10% of the class choose six points, then no one gets any extra credit.

YouGov has tested a similar question on the British public, offering either 20 or 100 free points (on top of the usual 50 rewarded for taking a YouGov survey) to respondents, with the same 10% threshold applying.

In the prisoner's dilemma, acting out of self-interest makes the participants worse off – which is the same problem British people have when responding to this generalised version. The threshold for everyone getting extra points is crossed four times – 41% choose 100 points, 59% choose 25 points.

Breakdown

People from London are the most likely group to choose 100 points. They divide 50%-50% between the cooperative and self-interested options, compared to people from the rest of the south who divide 61%-39%.

People who voted Lib Dem in May are the least likely to betray their fellow respondents, dividing 70%-30%, while people who voted Conservative divide 54%-46% – making them the second most likely to gamble on the side of self-interest.

Older people are more cooperative than young people, with 64% of over-60s choosing 25 points compared to 51% of 25-39s.

In the classic case, two members of a criminal gang are separately interrogated. The police don't have enough evidence to prosecute, so they offer them a deal. If both confess, they get 2 years in prison; if either confesses while the other remains silent, the snitch walks free while the other gets 3 years; if they both remain silent they both get 1 year. Clearly it would be best overall if they both stay silent, but there's always the risk that the other will confess, leaving you with a longer sentence, so in the end they both confess.

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See the full poll results