Estimating the Effects of Friendship Networks on Health Behaviors of Adolescents

Jason Fletcher, Yale University
Stephen Ross, University of Connecticut

This paper estimates the effects of friend’s health behaviors on own health behaviors for adolescents by comparing similar individuals who have the same friendship opportunities because they attend the same school and make the same friendship choices, under the assumption that the friendship choice reveals information about an individual’s unobservables. We combine this identification strategy with a cross-cohort, within school design so that the model is identified based on across grade differences in the clustering of health behaviors within specific friendship options. This strategy allows us to separate the effect of friends behavior on own behavior from the effect of friends observables attributes on behavior, a key aspect of the reflection problem. Our results suggest that friendship network effects are important in determining adolescent tobacco and alcohol use but are over-estimated in specifications that do not fully take into account the endogeneity of friendship selection by 20-30%.