In universities these days they play a lot of games - though when the economists play they prefer to call it ''game theory''. And game playing is one of the most potentially useful things academics do.

The most famous game played by social scientists is ''the prisoner's dilemma''. As described by Wikipedia, two suspects are arrested by the police. The police have insufficient evidence for a conviction, but they keep them separate and offer each the same deal.

If one testifies for the prosecution against the other (that is, ''defects'' from a position of solidarity with the other) and the other remains silent (that is, ''co-operates'' with the other), the defector goes free and the silent accomplice receives the full 10-year sentence.

If both remain silent, both are sentenced to only six months for a minor offence. If each betrays the other, each receives a five-year sentence. So each prisoner must choose whether to betray the other or remain silent.

Each is assured the other won't know about the betrayal before the end of the investigation. So how should the prisoners act?