The New York Times Magazine and Wired both have major articles this week on recent empirical work in social networks, including significant research on how things like obesity, smoking, and even happiness spread between among groups of people. The Wired piece has better pictures

while the NYT piece is more thorough and thoughtful, and covers both the potential and the pitfalls of this kind of analysis.

For decades, sociologists and philosophers have suspected that behaviors can be “contagious.” … Yet the truth is, scientists have never successfully demonstrated that this is really how the world works. None of the case studies directly observed the contagion process in action. They were reverse-engineered later, with sociologists or marketers conducting interviews to try to reconstruct who told whom about what — which meant that people were potentially misrecalling how they were influenced or whom they influenced. And these studies focused on small groups of people, a few dozen or a few hundred at most, which meant they didn’t necessarily indicate much about how a contagious notion spread — if indeed it did — among the broad public. Were superconnectors truly important? How many times did someone need to be exposed to a trend or behavior before they “caught” it? Certainly, scientists knew that a person could influence an immediate peer — but could that influence spread further? Despite our pop-cultural faith in social contagion, no one really knew how it worked.