The spread of health phenomena in complex, longitudinally resolved social networks

25 April 2008

Nicholas Christakis
Department of Health Care Policy
Harvard Medical School & Department of Sociology
Harvard Faculty of Arts and Sciences


Our work has involved the quantitative investigation of whether and how various health-related phenomena might spread from person to person in complex networks. We have developed various data sets to support these investigations, including a densely interconnected, longitudinally resolved network of 12,067 people assessed repeatedly from 1971 to the present. Each node in this network has an average of 11 ties of various kinds, including friends, siblings, spouses, offspring, coworkers, and neighbors. We observe discernible clusters of individuals with various traits, including obesity, smoking, eating, medication taking, and happiness, and we document that these clusters are not solely due to selective formation of social ties between nodes. Rather, processes of social contagion are also apparent within the network. Various aspects of our findings suggest that the spread of social norms is a key mechanism underlying these inter-personal health effects. In other work, we have examined the genetic basis for social network formation and have developed a novel model for the social processes involved (the "attract and introduce" model). The recognition of the role of supra-individual, network effects on individual health lays a further foundation for public health by providing a rationale for the claim that health is not just an individual, but also a collective, phenomenon


N A Christakis, J H Fowler, "The spread of obesity in a large social network in over 32 years", New England J Med 354:370-9 2007. PubMed. PDF

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