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The Collective Dynamics of Smoking in a Large Social Network (Full Text) 

Background The prevalence of smoking has decreased substantially in the United States over the past 30 years. We examined the extent of the person-to-person spread of smoking behavior and the extent to which groups of widely connected people quit together.

Methods We studied a densely interconnected social network of 12,067 people assessed repeatedly from 1971 to 2003 as part of the Framingham Heart Study. We used network analytic methods and longitudinal statistical models. . . .

Smoking behavior in contacts might influence smoking behavior in subjects by diverse biopsychosocial means, including changing the subject's norms about the acceptability of smoking, more directly influencing the subject's behaviors (e.g., a contact asking the subject not to smoke, or, conversely, a contact sharing cigarettes), or even fostering dependence through the inhalation of secondhand smoke. These mechanisms could not be distinguished on the basis of our data. We observed that geographic distance from a contact does not modify the effect of a contact's smoking behavior on a subject. This observation does suggest that social norms may be an important factor, since such norms may spread more easily over geographic distance than behavioral effects.

A change in the smoking behavior of more than one contact may be required for a subject to quit, and there may be additive or even threshold effects whereby a subject's probability of smoking cessation depends on smoking cessation by not one contact, but by two or more.30 This phenomenon may be especially likely in the case of smoking, since smoking is often deemed an explicitly social — and hence shared — behavior. Consequently, when a smoker runs out of easily available contacts with whom he or she can smoke, he or she may be more likely to quit. This possibility is also consistent with the group-level smoking cessation that we observed.

Network phenomena might be exploited to spread positive health behaviors.31,32,33,34 Indeed, cessation programs for smoking and for alcohol use that provide peer support — that is, that modify the person's social network — are more successful than those that do not.32,34 People are connected, and so their health is connected.35,36 Collective interventions may thus be more effective than individual interventions. Moreover, medical and public health interventions to encourage people to quit smoking might be more cost-effective than initially supposed, since health improvements in one person might spread to others.35,37,38 Finally, the isolation of smokers within social networks suggests that blanket policy approaches (e.g., advertising and taxation) may be usefully supplemented by interventions targeting small groups. In the case of smoking cessation in the past three decades, there is evidence of a cascade of salubrious behavior, and cessation of smoking in one person appears to be highly relevant to the smoking behavior of others nearby in the social network.

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