Cosma Shalizi on social contagion

Statistician and polymath blogger Cosma Shalizi is preparing a paper [1] on social contagion, basically dwelling on the fact that the transmission of behaviours through social influence ('contagion') is very hard to distinguish from the fact that similar people tend to be submitted to similar causal influences, and pair with people similar to themselves. Conversely, social contagion is easily mistaken for mere sociological determinism à la Bourdieu. All he's put online for the moment is a .ppt presentation - but a Powerpoint by Cosma Shalizi is worth a book by some others. Here.