Recent work also shows that some health outcomes can “spread” widely through social networks. For example, obesity increases substantially for those who have an obese spouse or friends (Christakis and Fowler 2007), and happiness appears to spread through social networks as well (Fowler and Christakis 2008). These findings suggest that the impact of social ties on one person’s health goes beyond that person to influence the health of broader social networks. Thus, policies and interventions should capitalize on this natural tendency for health-related attitudes and behaviors to spread through social networks by incorporating these amplification effects into the mechanics of interventions and their cost-benefit estimates (Smith and Christakis 2008).
