It's a tacky but frequent metric: comparing how many friends you have on Facebook. But when it comes to measuring how easily you can spread ideas or persuade new people to sign up, it turns out that the diversity of your friends and contacts is more important than their sheer volume.
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A study published in academic journal PNAS analysed 54 million invitations for people to sign up to Facebook. While it wasn't uncommon to receive multiple invitations, especially during Facebook's growth phase, the analysis suggested that sheer volume wasn't the best predictor of whether people would sign up:
In effect, it is not the number of people who have invited you, nor the number of links among them, but instead the number of connected components they form that captures your probability of accepting the invitation.
In other words: if you're asked separately to join by a workmate, a schoolfriend and a family member, that makes it more likely you'll join than if you just get bombarded with information from one group.
The big lesson? It's not just who you know, but the different kinds of people you know — a useful lesson to apply outside Facebook as well. If you don't interact with a diversity of people, it's easy to become angry and bitter and limited in your views. Just try listening to talkback radio if you don't believe that.