The Spread of Obesity in a Large Social Network over 32 Years

• https://www.nejm.org/doi/full/10.1056/NEJMsa066082
• Nicholas Christakis, James Fowler

Sparked heated debates about Homophily and influence and Causal inference with observational data.

Shalizi2011homophily argues that the methodology (or pretty much any observational study) cannot tease the homophily and influence out.