There’s been a lot of discussion, backed by some evidence, that groups are ‘smarter’ than the individuals in them, that groups make better decisions than individuals. But it is not, of course, as simple as that, and a recent study speaks to the limits of this principle. The study involved pairs of volunteers who were asked to detect a very weak signal that was shown on a computer screen. If they disagreed about when the signal occurred, then they talked together until they agreed on a joint decision. The results showed that joint decisions were better than the decision made by the better-performing individual (as long as they could talk it over).
However, when one of the participants was sometimes surreptitiously made incompetent by being shown a noisy image in which the signal was much more difficult to see, the joint decisions were worse than the decisions of the better performing partner. In other words, working with others can have a detrimental effect if one person is working with flawed information, or is incompetent but doesn't know it. Successful group decision-making and problem-solving requires the participants to be able to accurately judge their level of confidence.
(2010). Optimally Interacting Minds.
Science. 329(5995), 1081 - 1085.