GORE-TEX, the maker of water resistant jackets and outerwear, famously caps the number of employees per factory at 150, even if that means building two factories right next door. The company adopted this policy because they discovered that when the factory gets too big, people working for the company become much less likely to work hard and help each other out. When that happens morale goes down, and so do profits.
Research by anthropologist Robin Dunbar supports this rationale. Dunbar correlated brain size of different primates with the size of their social groups and extrapolated these results to humans. His research indicates that 150 represents a “magic number” for humans and the number of meaningful relationships they can maintain at one time.
We have spent many years studying online communities and believe Dunbar’s number is applicable to online communities as well. If a group is too small there isn’t much interaction. But as the group hits the critical mass of more than 100 visits per day, activity starts to pick up. As traffic exceeds 200, 300, 400, or more visits per day then it becomes necessary to institute more restrictive rules.
A bigger forum is usually better because it benefits from the network effect but there is something to be said about small, close-knit communities. Benefits from the network effect typically offset the loss of intimacy but we also note that engagement on a per user basis tends to drop as a forum grows in size. Our experience suggests smaller communities have more camaraderie and users offer each other more support. We doubt that Dunbar would be surprised.