Ego-centric analysis of social networks

I just had a course in Social Neworks Studies, which presented people as vertex and their relations as links between them. We had to make ego-centric analysis of three people around us, which ended nowhere, but in the end it was fun to do.

I liked the course, since it helped me understand how much one can learn from just looking at relationships between people, projects, events, etc.. For exemple, how much you can conclude from knowing who communicates with whom and how often, without really knowing the contents of the messages...

But apart from this, it also helped me understand this comics, posted on xkcd.com a few weeks ago:

... with the following text: Check it out; I’ve had sex with someone who’s had sex with someone who’s written a paper with Paul Erdős!