How do behaviors spread through social networks? Harnessing the new opportunity offered by social media, our research pioneered the use of online technologies to investigate the effects of social structure on the spread of health behaviors. Using experimentally controlled online health communities, we recruited over 1,500 people to join a health website, called “The Healthy Lifestyle Network,” in which participants were embedded into anonymous, Internet-based networks. Once participants joined the study, they were randomized into one of two network conditions – one community was designed with tightly clustered, “strong tie” networks, and one was designed with randomly structured “weak tie” or “small world” networks. A subject’s “neighbors” within her randomly assigned social network constituted his or her “health buddies” – i.e., other members of the online community from whom participants could receive information about new health behaviors, and to whom they could send notifications about behaviors that they adopted.
We introduced a novel online health tool into each of the twelve online networks via a “seed” actor, and observed the real-time diffusion of adoption through each of twelve independent communities. In every trial, the behavior spread to a greater fraction of the population in the clustered social networks than in the small world networks (on average, 54% of participants adopted in the clustered networks, while only 38% of the population adopted in the randomized small world networks). Moreover, in all trials the behavior spread faster in the clustered networks than in the small world networks. Finally, the results also showed that commitment to the behavior, i.e., long term engagement, was significantly greater among members who had received reinforcing signals from multiple neighbors, provided by the clustered networks.