The test asked the groups to generate ideas on the same problem — in this case, how to improve the United Nations Security Council. In the first group, everyone received the same flat fee. In the second group, your reward depended on how many ideas you contributed. In the third group, your reward depended on how many ideas other group members added to your ideas in the discussion tree.
The results showed that the third group generated more ideas overall, more different streams of ideas and ideas that were more fully articulated.Read the rest here (text borrowed directly from Columbia's Ideas@Work).