Dunbar's Number

In my various readings on random topics, I often come across ideas and snippets of information that can be interestingly applied to the different things I'm involved with, and so sooner or later I was always bound to hit on something that's at least tangentially related to this project... in this case Dunbar's number.

Dunbar's number is 150. According to Peter Pirolli from PARC, 150 is "the theoretical limit of the number of people that you can “know socially” in the sense that you know them as individuals and know something about their relations to one another (and you)".

I wonder if this beings to explain why most people on Facebook have somewhere between 150 and 250 friends - something I noticed after the initial feeling of competitiveness everyone has when they first join! If I discounted the number of people I've politely accepted as a 'friend' but can't honestly say I keep up with in any way, I'd be pretty close to Dunbar's number myself.

What's interesting is that in terms of building a network for this project it gives us an idea of the size of our existing close links, i.e. the number of people whose knowledge we can directly tap in to through the members of our Facebook group. Right now there's about 100 members in the group. Even if we accounted for a hugely optimistic 10% overlap of friends between all members, that still gives us (100*150)*(0.9) which is 13,500 people, and all it took was a few friends joining a group over a period of a couple of weeks. How amazing is that?