Why two heads really are better than one

But another finding might make the Conservative and Liberal Democrat coalition leaders pause for thought.

Solving problems together only works when both partners are equally competent and freely discuss their disagreements, say the research authors.

British and Danish scientists got their heads together to look at what happens when two people pool information to carry out a judgment task.

Pairs of volunteers in a laboratory were asked to detect a weak smudge on a computer screen.

If they disagreed about when the signal occurred, they talked until a joint decision was reached.

The first results showed that joint decisions were more accurate than those made by the better-performing individual alone. Two further tests confirmed that success depended critically on partners being able to talk the problem over.

But a fourth experiment showed that coalitions can be disastrous when partners are mismatched.

In this case, events were manipulated to make one of the volunteers appear incompetent but this was not known to the other partner, who continued to trust the first volunteer's judgment.

Joint decisions were then worse than the decision of the better-performing partner.

Professor Chris Frith, of University College London, one of the researchers whose findings are published in the journal Science, said: "When two people working together can discuss their disagreements, two heads can be better than one.

"But, when one person is working with flawed information – or perhaps is less able at their job – then this can have a very negative effect on the outcome."