Sourced with compliments from http://www.spring.org.uk/2009/08/why-groups-fail-to-share-information-effectively.php
In 1985 Stasser and Titus published the best sort of psychology study. Not only does it shine a new light on how groups communicate and make decisions, it also surprises, confuses and intrigues. Oddly, the results first look as if they can’t be right, then later it seems obvious they are right, then attention turns to what can be done about it.
The findings were relatively straightforward and, as is often the case with decision-making research, another blow for the fragile human ego. They found that people trying to make decisions in groups spend most of their time telling each other things that everyone already knows. In comparison people are unlikely to bring up new information known only to themselves. The result: poor decisions.
As it happens Stasser and Titus’ (1985) participants were making a relatively trivial decision—who should be student body president—but subsequent research has tested all sorts of other scenarios. Experimenters have asked people to choose the best candidate for a job (Wittenbaum, 1998), the best type of investment (Hollingshead, 1996) and the guilty party in a homicide investigation (Stasser & Stewart, 1992).
Again and again the results have shown that people are unlikely to identify the best candidate, make the best investment or spot who really committed the crime. When asked to make a group decision, instead of sharing vital information known only to themselves, people tend to repeat information that everyone already knows.