Is Five the Magic Number?

April 17, 2009

Over at InfoQ, Vikas Hazrati has aggregated some interesting thoughts on the ideal size of a Scrum team. While Scrum literature advocates teams of seven plus or minus two, Hazrati’s evidence suggests that, in fact, it’s groups of five that perform the best.

Now, we already know that as the number of team members increases, the channels of communication go up exponentially. So it’s hardly surprising to hear that a team should not be larger than nine. But why five? Hazrati offers some interesting reasons.

According to a blog post on Cognitive Edge, five—and increments of five—play an unusual role in creating natural limits for human groupings. The author suggests that this phenomenon is directly linked to how the human brain has evolved in relation to social conditions.

So what’s the big deal with five? As the blogger points out, “five is linked to the natural limits on the short term memory.” That is, the number is applied to time, rather than objects or persons. Five minutes of instruction might lead a team to complete a task with astounding focus, but if the same team receives its direction stretched out over an hour, it’s unlikely that the team will respond in the same way. Likewise, activities that require five or fewer steps are easy to remember, but if they require more, the user will need a cheat sheet. (The blogger goes on to explain how 15 is related to the number of individuals one can trust deeply, while 150 relates to the total number of individuals or acquaintances a person can hold in his mind. Though fascinating, these points seem much less relevant to a discussion to the ideal size of a Scrum team.)

Certainly, five hits the sweet spot for short-term memory and few communication channels, but can the ideal size of a Scrum team ever really be absolute? Well, Jurgen Apello, who also believes that five is the ideal Scrum team size, backs down a little in the end, explaining, “When you need to structure a big project, don’t impose a “preferred” team size on people just because it is written in a book. Try to allow self-organization to do its job and let the people (within their real environment) figure out what their optimum is.”

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