Ideal Team Size: Is there a magic number?

I've been doing some research lately on the relationship of team size to overall performance. Much depends on the nature of the work, but one thing seems consistently clear. Small teams are more effective, less likely to lapse into complacency, and more likely to engage all members. But how small?

2 is not enough diversity and/or can lead to a stalemate. 4 can lead to taking sides. 3 is arguable. In one sense there's adequate diversity with 3, and it's easier to reach a majority. It's also easy to maintain frequent communication. Yet some evidence shows that it may not be enough critical mass to keep momentum going.

My friend and colleague Ken Thompson of BioTeams suggests that 5-9 people is the ideal team size, and that large teams should be broken into sub-teams of that size. Here's his blog post on the topic, which references some interesting articles, plus one where he talks about the "hidden sub-team" that often exists but we don't recognize.

http://www.bioteams.com/2006/01/13/the_maximum_team.html

Also, here's an interesting article from Wharton's knowledge center. It, too, seems to support the small teams concept, even referencing a theory that 6 is the magic number. It also talks about diversity. We all know the importance of diverse perspectives on our team, but is there a such thing as too much diversity? Food for thought.

Here's the article.

http://knowledge.wharton.upenn.edu/article.cfm?articleid=1501