On March 17, 2008, PED Seminar Series Presents

Eat, Drink, and Be Merry: The Spread of Health Phenomena in Complex, Longitudinally Resolved Social Networks

by Prof. Nicholas Christakis

Our work has involved the quantitative investigation of whether and how various health-related phenomena might spread from person to person. For example, we explored the nature and extent of person-to-person spread of obesity. We developed a densely interconnected network of 12,067 people assessed repeatedly from 1971 to 2003. We used longitudinal statistical models and network-scientific methods to examine whether weight gain in one person was associated with weight gain in friends, siblings, spouses, and neighbors. Discernible clusters of obese persons were present in the network at all time points, and the clusters extended three people deep. These clusters were not solely due to selective formation of social ties. A friend becoming obese in a given time interval increased a person's chances of becoming obese by 57% (95% CI: 6%-123%). Among pairs of adult siblings, one becoming obese increased the chance that the other became obese by 40% (21%-60%). Among spouses, one becoming obese increased the likelihood that the other became obese by 37% (7%-73%). Among those working in small firms, a co-worker becoming obese increased a person's chances of becoming obese. Immediate neighbors did not exhibit these effects. We have also conducted similar investigations of other health behaviors, such as smoking, drinking, exercising, and the receipt of health screening, and of other health phenomena, such as happiness and depression. Various aspects of our findings suggest that the spread of social norms may partly underlie inter-personal health effects. Our findings have implications for clinical and public health interventions, and for cost-effectiveness assessments of preventive and therapeutic interventions. They also lay a new foundation for public health by providing a rationale for the claim that health is not just an individual, but also a collective, phenomenon.

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