January 16th, 2007
What is Dunbar’s Number?
by Joshua Porter | 
10 Comments
Dunbar’s Number, proposed by British Anthropologist Robin Dunbar, measures the “cognitive limit to the number of individuals with whom any one person can maintain stable relationships”.
The number, which approximates to 150, would seem to have important implications for social design.
- It suggests that there is an upper-limit to the number of meaningful relationships we can cultivate, either online or off. Most likely the number would be different for everyone, but at least acknowledging a limit can be healthy because it keeps down pie-in-the-sky visions of what people do. It’s always good to remember that we have limits.
- It suggests that a lot of the activity on social sites isn’t really about “stable relationships”. It should be clear, but isn’t always, that 845 connections on LinkedIn aren’t really friends or even associates. Most of the social ties, if they even exist, are much looser than that. So though the number is high, it might not mean that the person is well-connected more than it means they’re hungry for a high number of connections. So Dunbar’s number, even if it is off by 100, is yet more indication that the social relationships on sites aren’t what they always appear to be. The question becomes: what kind of relationships are they?
Dunbar came up with the number after studying other primates and then applying that knowledge to humans. He verified it, so to speak, by analyzing the number of people in various social groups around the world and in different situations. For example, he found the size of certain tribal villages to be about 150.
Similar to the Magical Number 7, it would be easy to misapply Dunbar’s Number. For example, I can imagine systems being built to allow only a certain number of contacts, for example. That’s an extreme case, but given what extremes people go to stick to numbers it wouldn’t surprise me.
Nevertheless, Dunbar’s Number might be good to keep in the back of the mind in order to stay reasonable.
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Bokardo is a blog about interface design for social web sites and applications. I write about recommendation systems, identity, ratings, privacy, comments, profiles, tags, reputation, sharing, as well as the social psychology underlying our motivation to use (or not use) these things. If this sounds interesting to you, grab my RSS Feed. If you want to know more about me, check out my about page.
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Comments ( 10 Responses so far )
1. ~bc 9:15am, Tue 16th, 2007
Should sites like MySpace have an upper limit of friends you can add? Sort of like your top four/eight/16, but less so… it would force you to actually think instead of just “thanks for the add…”
2. Jeff Watkins 10:11am, Tue 16th, 2007
You know, one of the slightly unsatisfactory things about sites like LinkedIn is the inability to rate a connection. For example, I’ve got a connection to some guy who worked at BroadVision at about the same time I did, but I don’t know him particularly well. So when it comes to introductions, the system shouldn’t really count on that connection, because it’s tenuous at best.
Of course, I _could_ make an effort to strengthen the connection. That would probably be mature and forward thinking on my part…
3. Mark 2:54pm, Tue 16th, 2007
Dunbar’s number is very interesting in that it applies to a wide range of organizations from a number of different perpsectives. For example, John Robb has applied the concept to terrorist networks:
http://globalguerrillas.typepad.com/globalguerrillas/2004/03/what_is_the_opt.html
And I believe Malcolm Gladwell explored the concept in The Tipping Point (it’s been a while since I read that, but I think he mentioned something about a company that would limit their offices to 150 people).
With respect to social web apps, I think the interesting thing is how some of them are able to bypass the limit to produce a useful information resource. For example, del.icio.us aggregates bookmarks and tags in such a way that many more than 150 people can contribute to the resource without experiencing the degradation that Dunbar’s number suggests.
4. David Sanford 12:29am, Wed 17th, 2007
First of all, thank you Joshua for the interesting post and for your blog more generally (I’ve been an active reader for some time now).
Jeff - We at LinkedIn (click my name for more on my role there) obviously think about these issues on a regular basis. We recommend that people only accept connection requests from people with whom they already have a relationship or for whom they would at least feel comfortable saying something positive if asked, say, as part of a reference check. LinkedIn should be an extension of your real-world relationships, not a substitute.
We’ve also been thinking about ways to add context to connections on LinkedIn, both privately and publicaly, and would be open to your suggestions.
Finally, you can always disconnect from people with whom you no longer have a relationship.
Looking forward to more great thoughts on this blog,
Dave
5. Michael Chui 4:53am, Wed 17th, 2007
The common misconception about the Dunbar Number is that it applies to your own system: people shouldn’t design systems assuming that 150 will be the cap. More likely, a tight social network will end up closer to 25 or 50.
This is the oldest and best post I know on the subject: Life with Alacrity: The Dunbar Number as a Limit to Group Sizes. I also found this post “Great Social Networking Posts,” but I couldn’t locate the one I was looking for, which slashed the optimal numbers to 12, 50, and 150. It was by someone else in the blogosphere… it’s been too long.
6. Josh 9:45am, Wed 17th, 2007
Michael…thank for the link! Looks like a great resource…
7. Christopher Fahey 5:52pm, Sat 27th, 2007
A friend of mine who worked on a very major social networking product told me that they had actually used the 150 cap for their users’ connections lists — at least initially. What they found was that, while Dunbar’s number is valid for most people, it completely demolished the impact of “superconnectors”, who are the ultra-well-connected people who make up the real power base of social networks. Superconnectors have hundreds of connections — real connections, people they know. They exist in the real world, too, not just virtually, and they keep our societies together.
IMHO, Dunbar’s Number sounds even more like the Magical Number 7 than you seem to suggest: That is, it’s almost completely useless and irrelevant to real-world design decisions.
8. Tim 2:36pm, Wed 14th, 2007
Mark… If I remember correctly, the company you’re thinking of (Gladwell’s example), is Goretex.
Tim.
9. johny 6:22am, Wed 28th, 2007
You know, one of the slightly unsatisfactory things about sites like LinkedIn is the inability to rate a connection. For example, Tworzenie stron www I’ve got a connection to some guy who worked at BroadVision at about the same time I did, but I don’t know him particularly well.
10. Gregy 6:02pm, Fri 20th, 2008
Jeff - We at LinkedIn (click my name for more on my role there) obviously think about these issues on a regular basis. We recommend that tworzenie stron only accept connection requests from people with whom they already have a relationship or for whom they would at least feel comfortable saying something positive if asked, say, as part of a reference check. LinkedIn should be an extension of your real-world relationships, not a substitute.