The Influence of Peer Genotypes and Behavior on Smoking Outcomes : Evidence from Add Health

We introduce a novel use of genetic data for studying social influences on behavior: Using data from the National Longitudinal Study of Adolescent to Adult Health (Add Health), we deploy the distribution of genotypes in a given grade within a school to instrument the influence of peer smoking on an individual's own smoking behavior. We argue that this design alleviates many problems inherent to estimating peer effects. Using this approach, we find the relationship between peer smoking and individual smoking to be larger than that estimated by prior studies. Further, we explore the reduced form relationship between peer genotypes and ego smoking and find that the impact of peers' genetic risk for smoking on ego's smoking behavior is at least half as large as the effect of individual's own genotype and sex, and 30% the effect of age. Moreover, peer influence on smoking appears heterogeneous by race: although whites and non-whites are equally susceptible to peer influence with respect to smoking, white egos are more likely to be influenced by white alters. This analysis suggests a promising way that genetic information can be leveraged to identify peer effects that avoids the reflection problem, contextual effects and selection into peer groups