Connected, by Nicholas Christakis and James Fowler, (ISBN 978-0-00-734743-8) is a fascinating study of social networks. In the Preface they write
To know who we are, we must understand how we are connected.
This is what Clay Shirky says in Here Comes Everybody, it’s what Johansson says in The Medici Effect, Andy Clark says in Smart World, and, for me, most powerfully what Barabasi says in Linked. So what does this book add?
The clear focus of Connected is social networks – you’ll be familiar with the idea of “six degrees of separation” where it’s been discovered there are an average of only six steps between any two human beings on the planet. Christakis and Fowler take this finding a step further by highlighting and explaining “three degrees of influence”. In social networks, you influence your friend, who influences their friend, who influences their friend (and the influences flow both ways), but after that, the power of the effect tails off or disappears. The power of the effect seems related to two things – how many connections a person has, and how many of those people to whom they are connected are connected to each other (in other words how many of your friends know each other?)
These simple characteristics create very complex webs and patterns of influence and can explain a wide range of events, from the spread of a viral infection in a community, to the collapse of the financial system, to the spread of obesity, a wide range of disorders, and both cultural and political changes.
It’s a bizarre thought to learn that obesity in a community is distributed the same way as an infection. If your friend’s friend becomes obese, you’re more likely to become obese (and vice versa)! Obesity seems to be contagious.
The book is packed full of interesting and mind-boggling examples. A couple that really struck me were the spread of back pain in Germany – before the wall came down East Germany had a very, very low incidence of back pain, and in the West it was one of the highest rates in the world. After the wall came down, the incidence in the East rose to match that in the West. A study of epidemic control showed that you needed to vaccinate 90% of the population to stop the infection, but if, instead you asked a random selection of individuals who their acquaintances were, then calculated which individuals were most connected, and vaccinated only them, you could control the infection by vaccinating only 30% of the population. I could go on…..but read it yourself, it’s truly mind expanding. Really the idea that we are all separate free-thinking individuals is at best a simplistic delusion. We are who we are because of the way we connect.