"Experiment after experiment has shown that people in brainstorming sessions produce fewer and lower quality ideas than those working alone (Furnham, 2000). Here’s why:
- Social loafing: people slack off to a frightening degree in certain types of group situations like brainstorming.
- Evaluation apprehension: although evaluation isn’t allowed in a traditional brainstorming session, everyone knows others are scrutinising their input.
- Production blocking: while one person is talking the others have to wait. They then forget or dismiss their ideas, which consequently never see the light of day.
…
Also it emerges that groups do have a natural talent, which is the evaluation of ideas, rather than their creation."
- found on http://hitenshah.name/