The Rules of Contagion

Initial retweets about the Higgs boson rumour, 1 July 2012. Each dot

represents a user, with lines showing retweets

Data: De Domenico et al., 2013

For infectious diseases, we’ve seen there are two extreme types of
outbreaks. ‘Common source’ transmission occurs when every one
gets infected from the same source, like food poisoning. At the other
extreme, a propagated outbreak spreads from person-to-person over
several generations. There is a similar diversity in online cascades.
Sometimes content will spread to lots of people from a single source

• known in marketing as a ‘broadcast’ event – whereas on other
  occasions it will propagate from user to user. The Stanford and
  Microsoft researchers found that broadcasts were a crucial part of the
  largest cascades. About one in a thousand Twitter posts got more
  than 100 shares, but only a fraction of these spread because of
  propagated transmission. Of the posts that spread, there was
  generally a single broadcast event behind its success.