Think about the benefits of a large group versus the ideal number of people. The more people you have, theoretically, the better chance you have of getting the best information to make the best decision. Research has shown that collective intelligence does exist. But, according to research reported in Science, the October 2010 issue by authors Anita Williams Woolley, Christopher F. Chabris, Alex Pentland, Nada Hashmi and Thomas W. Malone:

This “c factor” (the group’s collective intelligence) is not strongly correlated with the average or largest individual intelligence of group members but it correlates with the average social sensitivity of group members, the equality in conversational turn-taking, and the number of women in the group.

Emotional intelligence and soft skills are more important to the functioning of teams than focusing on the ideal number. Our assessment of the performance traits of the team members using SuccessFinder can create the needed diversity of thought for the team to be extremely effective.

Hackman and Vidmar (1970)

Moreover, their research on optimum group size for member satisfaction showed a similar outcome. They determined the ideal number was 4.6 members, let's call it 5. The number is just one factor. Social sensitivity and being able to read emotions are attributes of successful team decision-making. Consider the number and consider the members. Maybe they’ll need a little training in empathy and being sensitive to others as well as having a culture that allows all to fully take part.