A lot of organisations use group brainstorming as part of the strategy formulation process. The problem with group brainstorming is that, unless the group is not larger than 1, the outcome is not the best possible. There is a lot of research done on the effectiveness of group brainstorming vs nomial group (alone) brainstorming. The results show that in most cases the nomial groups produce a larger number of ideas and also produce a wider variety of ideas.

The reasons for these under performing groups are:

Evaluation apprehension(1): Group performance is impeded by the members' fears of being negatively evaluated by the other group members
Free-riding(2): Interactive group members suffer motivational deficits due to the members' feeling that their ideas are not necessary for the group to succeed
Production blocking(3): The decrease in group performance results from the inability of group members to state ideas freely and without interruption
Social influence(4): Individuals match their performance to that of the other group members

Since it is important that at the initial stages of the startegy process, or any other process that requires new ideas, the greatets number of ideas is generated how can organsations improve their brainstorming results?

Use a highly trained facilitator! Research (5) has shown that trained facilitators can reduce all of the above reasons for under performing groups. The trainers need to be trained and experienced. That will lead to more ideas being recognized and also more fully explored.
Use anonymous group brainstorming software! Group brainstorming software gives participants the oportunity and the abaility to enter ideas, votes, comments independently and anonymously.

Read more: Improve your organisational brainstorming