The answer would seem to be circumstantial. For traveling companions, one to four is often enough. My intimate circle of friends probably numbers only half a dozen. Still, when someone asks, I validate myself as having 131 Facebook friendships and 411 Linkedin connections.
Clearly, I can’t manage that many close, personal friends. So what is happening here?
On reflection, I think that I have various levels of affinity. Family and close friends probably number less than a dozen: these are people that I stay in touch with regularly, see face to face if I’m in the area, and send regular cards and emails.
Beyond this lie my neighborhoods and workgroups. They probably number about 20 each, and there are three or four of them These are active circles of people that I correspond with or talk with regularly, but in the context of works, school, neighbors, and people who I share some special interest with.
Continuing outward, there is a ring of perhaps a hundred people who I correspond with occasionally and would recognize if I met them. This is my ‘Christmas Card list’: almost all are members of former neighborhoods and workgroups. My Facebook group has a lot of these characteristics, and I see how I tend to accumulate this group of colleagues and associates throughout life.
There is a periphery of casual acquaintances that are one-time contacts or friends-of-friends that seem to pile up on LinkedIn. There are a lot of people in there that I don’t know well and never hear from.
Two of these numbers seem particularly universal.
The first is 10. Lots of management theory regarding the optimal size of workgroups or the number of direct reports that one manager should have conclude that 8 to 15 members is best. I suspect that the same holds for active friendships; it is about the limit of time, detail, and energy that we can give at that level to maintaining a social relationship. (I find that I also have about 10 to 20 blogs or tweeters that I follow, and regular readers of my blog and my tweetees number that size in return).
This idea was famously captured in the Mythical Man-Month: “Adding manpower to a late software project makes it later”. In flat organizational structures larger than 20, communications and coordination start to overwhelm productivity and execution.
In my experience, many organizations go through cultural change at similar power-of-ten growth thresholds. Each time a company goes through the barrier of 100 or 1000 employees, it adjusts by adding a layer of management. This, in turn, causes social dislocations as people’s reporting relationships get broken and reattached, and as distances between power centers increase.
The second is 150. This is Dunbar's number: the theoretical cognitive limit to the number of people with whom one can maintain stable social relationships. A tribe or neighborhood can be cohesive up to that size, but requires restricted rules, laws, and enforced norms to function on a larger scale.
The Economist had an intriguing article this week that applies this concept to social networking, finding that “friend lists” generally grow to include about 120 people. Interestingly, though, people still tend to interact more frequently with a much smaller circle of friends: no surprise that it’s in the range of 10 to 20.
I’m intrigued by the counterintuitive tendency for social groups to consolidate as they grow, though. Villages become 100,000 person cities rather than spawning more villages; companies become corporations with 10,000 employees instead of spinning-out smaller divisions. I wonder if over-optimal size is the cause of a lot of the rule-driven pathologies that seem to infect these larger social structures? Do smaller 150-person neighborhoods and tribes form within them? In town, I suppose I have my neighborhood of people and shops that I know; I’m not sure what the analogous company structure is.
Finally, I wonder how this applies to my current work on remote patient monitoring. If a single center tries to keep track of the health status of 1000 people, is that too large a group to understand no matter how well organized the summary reports are?
Traveling companions are a corner case; four is the comfortable limit for a car, hotel room, or airline budget. Sometimes, though, even one can too, too many for a solitary morning walk or reflecting over an evening’s sunset.