If you aren't familiar with Scrum, it's a methodology that IT teams use for Agile software development. It has some basic tenets and subscribes to the core essentials of the Agile Manifesto. As I have learned more and more about Scrum, I have started to see patterns that I think could be applied across other departments as well.
One of those areas is organizational design and team size. Scrum originally recommended a team size of seven, plus or minus two, so five to nine individuals. From what I can gather, that number was really based on a psychology paper by George A. Miller called "The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information." If you want, you can
download the paper here for personal use from the University of Toronto. Miller's basic premise is that humans have a natural upper bound for being able to keep concepts in working memory, and that upper bound is, in many cases, nine. Alongside that, seven items are truly in a sweet spot of sorts. If you don't want to read the paper, but are interested in Miller's Law, you can read the
Wikipedia synopsis here.