Spread of obesity through social networks

Obesity is probably not contagious

A 2007 research paper in the New England Journal of Medicine tracked the spread of obesity in a large social network over 32 years and claimed that obesity spread through social networks. That is to say, having obese friends put you at risk of becoming obese yourself.

The results of that study are disputed in a later paper:

It is well known in the economics literature that failure to include contextual effects can lead to spurious inference on “social network effects.” We replicate the NEJM results using their specification and a complementary dataset. We find that point estimates of the “social network effect” are reduced and become statistically indistinguishable from zero once standard econometric techniques are implemented. We further note the presence of estimation bias resulting from use of an incorrectly specified dynamic model.