In the movie The Magnificent Seven, a group of crusty gunfighters led by Yul Brynner successfully protects a small Mexican village from desperadoes. The movie itself is a remake of Akira Kurosawa's Seven Samurai.
As it turns out, seven is a great number for not only forming an effective fictional fighting force, but also for task groups that use spreadsheets instead of swords to do their work.
That's according to the new book Decide & Deliver: 5 Steps to Breakthrough Performance in Your Organization (Harvard Business Press).
Once you've got 7 people in a group, each additional member reduces decision effectiveness by 10%, say the authors, Marcia W. Blenko, Michael C. Mankins, and Paul Rogers.
Unsurprisingly, a group of 17 or more rarely makes a decision other than when to take a lunch break.
Larger groups only seem to work when they adopt a strict set of governing policies, such as spelling out when a majority is needed to ratify a decision versus a plurality. But just getting agreement on those policies alone can be several meetings worth of work.
So my advice: If you have a choice when forming a group, limit membership to seven or less. And choose Yul Brynner as your team lead.