Does Your Group Pass the "Two Pizza" Test?
Are we hard wired to function best in teams of a certain size? Some scientists and business leaders think our cognition and performance suffer when a team gets too big.
In their book Connected: the Surprising Power of Social Networks and How They Shape Our Lives, Nicholas Christakis and James Fowler discuss the work of psychologist Robin Dunbar, who studied the size of different kinds of human groups. The basic Roman army unit was 120 men, and armies throughout many centuries have had 150 men in a unit. Analogous modern armies tend to be about 180 soldiers. Those numbers suggest that despite technological advances, there's an upper limit to the size of a group in which members can function in a coordinated, comprehensive way. Dunbar identified four as the optimum size for a human conversational group, and Connected authors say other researchers studying restaurant patrons, dinner parties and beach goers found people tend to gather in conversational clusters of four.
So what's the right size for a group assembled to launch a product or a sales campaign, to do research, or seek innovation? Rich Karlgaard, in a piece in "Forbes" magazine, advises "Think (Really) Small." Karlgaard notes Amazon founder and CEO Jeff Bezos, advocates the "two pizza rule" for team size. A group that needs more than two pizzas is too big, Bezos has asserted. Bezos thinks people communicate more effectively and productively in small groups, and get more done more quickly. In her management blog, Janet Choi describes some of the science behind this idea, and it supports Dunbar's finding that there are limits on the numbers when it comes to effectiveness in groups of people working closely together.
Karlgaard and Choi explain that the issue is how we manage all the connections between and among people, and organizational psychologists have come up with a formula that shows how the complexity of the network expands exponentially with each additional member. If you multiply the number of people in a group by that number minus one, and divide by two, you'll see the number of links or connections. Karlgaard provides a chart:
2 members = 1 connection
3 members = 3 connections
4 members = 6 connections
6 members = 15 connections
16 members = 256 connections
32 members = 1,024 connections
Karlgaard says if a team reaches 1,500 members, and some big company divisions do, the number of interconnections reaches 2.25 million. Our brains can't handle that, and in very large groups, relationships tend to degrade. Choi quotes research suggesting that people in very large teams are more stressed, work more slowly, and are more vulnerable to miscommunication and misinformation.
Researchers and business leaders vary on optimum size, but most advocate keeping working team membership in the single digits. The Two Pizza rule means it's six or seven. Organizational psychologist J. Richard Hackman likes five and he says don't have more than 10. Management expert Bob Sutton says the U.S. Navy Seals consider four people the optimal number for a combat team."