If your friends were normal people they would not know you.

"Your friends are unusual people", says physicist Mark Newman: simply because they are someone's friend. Newman is exploring social networks. More specifically, he wants to know what the chances are that we have a friend of a friend who supports ... the New York Giants. Or who went to Florence last summer. Or who likes water polo. ... [E]stimating how many friends of friends fall into a particular group is hard, because the structure of the social network is complex. For example, each of our friends doesn't just have a circle of other friends unknown to us, plus us. Rather, we share mutual friends. And two of our friends who share a mutual friend not known to us probably know each other too. It is a tangled web. ... He has devised a mathematical approximation for coping with ... biases. It makes a more accurate estimate of the number of 'friends of friends' that fall into a particular subset of the population.