Let's gather together and figure it out why.
The results were telling. The brainstorming groups slightly outperformed the groups given no instructions, but teams given the debate condition were the most creative by far. On average, they generated nearly twenty per cent more ideas. And, after the teams disbanded, another interesting result became apparent. Researchers asked each subject individually if she had any more ideas about traffic. The brainstormers and the people given no guidelines produced an average of three additional ideas; the debaters produced seven. New Yorker