"Also it emerges that groups do have a natural talent, which is the evaluation of ideas, rather than their creation."

Brainstorming Reloaded | PsyBlog Unintentionally, casts a light on how and why online innovation communities like the IdeaExchange work.:

“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:
  1. Social loafing: people slack off to a frightening degree in certain types of group situations like brainstorming.
  2. Evaluation apprehension: although evaluation isn’t allowed in a traditional brainstorming session, everyone knows others are scrutinising their input.
  3. 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.
So if groups need to generate new ideas, new connections between old ideas and new ways of seeing the world, how should they proceed? The answer is that brainstorming needs a tweak.”