Tomas Chamorro-Premuzic, Why Group Brainstorming Is a Waste of Time, Harvard Business Review, March 25, 2015:
A meta-analytic review of over 800 teams indicated that individuals are more likely to generate a higher number of original ideas when they don’t interact with others. Brainstorming is particularly likely to harm productivity in large teams, when teams are closely supervised, and when performance is oral rather than written. Another problem is that teams tend to give up when they notice that their efforts aren’t producing very much.