Estimating Heterogeneous and Hierarchical Peer Effects on Body Weight Using Roommate Assignments as a Natural Experiment

We investigate peer effects in weight gain by exploiting a natural experiment, roommate assignments of 751 male and 845 female first-year college students. Results indicate that females are subject to peer influence in weight gain, with little evidence of peer effects for males. Peer influences appear to be heterogeneous as heavier and thinner females are affected by roommates more than average-weight females, and hierarchical with females influenced only by roommates who are thinner, of a higher socioeconomic status, and more sexually experienced relative to themselves. Similarity of academic performance, religiosity, and political views appears to facilitate transmission of peer influences.