Using Facebook to assess the size of social networks

There are some people who argue that the Internet increases the size of people's social networks by lowering the transaction costs of interacting with people.

Facebook -- as a dataset -- is handy for determining whether this is true. Everyone on Facebook has friends with whom you communicate on a regular or irregular basis. Therefore, it could allow you to quantify the size of social networks on the Internet.

This is precisely what Cameron Marlow, a sociologist at Facebook, did at the prompting of the Economist.

Marlow looks at the size of social networks on Facebook in terms of friend list size and the rate of communication between those friends. The Economist relates those findings to the Dunbar number -- a number posited by anthropologist Robin Dunbar to represent the upper limit in the size of a primate's social group due cognitive costs.

From the Economist article:

Several years ago, therefore, Robin Dunbar, an anthropologist who now works at Oxford University, concluded that the cognitive power of the brain limits the size of the social network that an individual of any given species can develop. Extrapolating from the brain sizes and social networks of apes, Dr Dunbar suggested that the size of the human brain allows stable networks of about 148. Rounded to 150, this has become famous as "the Dunbar number".

Many institutions, from neolithic villages to the maniples of the Roman army, seem to be organised around the Dunbar number. Because everybody knows everybody else, such groups can run with a minimum of bureaucracy. But that does not prove Dr Dunbar's hypothesis is correct, and other anthropologists, such as Russell Bernard and Peter Killworth, have come up with estimates of almost double the Dunbar number for the upper limit of human groups. Moreover, sociologists also distinguish between a person's wider network, as described by the Dunbar number or something similar, and his social "core". Peter Marsden, of Harvard University, found that Americans, even if they socialise a lot, tend to have only a handful of individuals with whom they "can discuss important matters". A subsequent study found, to widespread concern, that this number is on a downward trend.

The rise of online social networks, with their troves of data, might shed some light on these matters. So The Economist asked Cameron Marlow, the "in-house sociologist" at Facebook, to crunch some numbers. Dr Marlow found that the average number of "friends" in a Facebook network is 120, consistent with Dr Dunbar's hypothesis, and that women tend to have somewhat more than men. But the range is large, and some people have networks numbering more than 500, so the hypothesis cannot yet be regarded as proven.

What also struck Dr Marlow, however, was that the number of people on an individual's friend list with whom he (or she) frequently interacts is remarkably small and stable. The more "active" or intimate the interaction, the smaller and more stable the group.

Thus an average man -- one with 120 friends -- generally responds to the postings of only seven of those friends by leaving comments on the posting individual's photos, status messages or "wall". An average woman is slightly more sociable, responding to ten. When it comes to two-way communication such as e-mails or chats, the average man interacts with only four people and the average woman with six. Among those Facebook users with 500 friends, these numbers are somewhat higher, but not hugely so. Men leave comments for 17 friends, women for 26. Men communicate with ten, women with 16.

The debate over the actual value of the Dunbar number is, I think, beside the point. This data is interesting to me because it seems to show that a) there is an upper limit to the number of people in a social network and b) that most people's core network is much smaller than that limit.

Anyone who has spent much time on Facebook probably understands this experience: you have a lot of "friends" on Facebook that are not really friends in the strictest sense. Setting aside your boss -- who you are obligated to friend but who you don't allow to see anything other than your name -- there are a lot of passing acquaintances on your friend list. Maybe you met them at a party once two years ago and don't feel comfortable doing wholesale purges of your online retinue.

The Internet has brought me in contact with all manner of interesting people. With some of them I have struck up more lasting friendships. But at some point you begin to realize that you only have so many hours in the day, and you have to decide whom in your life you want to keep track of. The Internet -- while wonderful in many ways -- is unlikely to change that.

But this realization is revealing. The core issue is: what are the specific transaction costs of keeping a relationship? What is all that effort going towards?

I would argue that the cost the transaction costs of keeping track of someone is not primarily the effort of actually speaking with them. Rather, it is the cost of remembering their name, what they do, what they think, and how they have related to you in the past. Just because the Internet has lowered the cost of talking with someone doesn't make it easier to remember all this information. (I guess you could make a system that does, but if it exists I don't know about it.)

Anyway, I think this study is particularly compelling because it illustrates that cognitive costs of social interactions are probably more about memory than about the actual effort of meeting.


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Curiously interesting stuff. A couple things.

Facebook isn't an exact science. For example, I created an account for the purposes of running a Group. That account eventually accumulated 42 friends, none of whom am I actually friends with, and I don't interact at all with any of them. And I'm still a Facebook novice (the real me is not actually on Facebook), having only accepting the friend requests because I saw no harm in it (and possible gain re: the Group).

It seems to me that social networks are more driven by need than anything else. So the average size of core groups has more to do with how many close friends a particular personality type needs in order to feel fulfilled, etc., and the same for wider social networks to an extent, but the farther out from the core of the network the more other motivations for maintaining acquaintances come in to play, such as maintaining physical wellbeing through work/trade relationships etc. So for example, were I independently wealthy, my wider social network would likely shrink.

I'm reminded of the guy whose job it is to remember who everyone is and whisper their names into the king's ear just before the king greets them. Or better, the whole business of announcing a guest's name and title as they enter the room. It wasn't to honor them; it was so everyone could remember who they were.

It seems to me that there is a tendency to collect friends, to get as many people to be your friend as possible. You get bragging rights for having lots of friends. I have "friends" with whom I have had no contact what-so-ever, only the request to be friends.

Chow! :)

By Sweetwater Tom (not verified) on 27 Feb 2009 #permalink

It seems like tools are a big part of the change. If we can access them, afford them and understand how, and why to use them. Their potential for technology to help us get smarter how to build and convey the value of content products is tremendous. With engagement as the sweet spot. But the rules of engagement have changed, with dozens of ways the term is applied. While not the size of Facebook, Twitter is growing very large, ... The most important thing if you're using a Twitter account for a business is to ... There you have it folks, your daily social media advice from the Facebook!!

on the profile vs fan page it depends how you want to use Facebook really.If you want to keep in contact with friends, arrange events and share snapshots of friends a profile is the most useful.If you want to have a Tet Zoo presence on Facebook a fanpage is less personal but still allows you to post links and photos as well as people being able to 'become a fan' of Tet Zoo and talk on the wall.