Many people assume that "several heads are better than one," but is that necessarily true? In many studies conducted, it actually demonstrates that individual brainstorming is more effective than group brainstorming because groups tend to come up with fewer and less creative ideas than individuals. Groups also often overestimate how successful they are at producing new ideas, which may explain why brainstorming is so popular. If someone thinks that they are creating brilliant ideas by combining brainpower, they are most likely to continue brainstorming within a group. However, below are two reasons why group brainstorming is less effective than individual brainstorming.
1.) group members may be anxious about being evaluated by others, leading them to hold back potentially good ideas.
2.) When brainstorming in groups, people frequently tend to "free ride" : They sit back and let others do the work, while they still get credit for the group as a whole. (Also could be called social loafing, a phenomenon in which people slack off in groups)