Searching for Peer Group Effects: A Test of the Contagion Hypothesis

Laura M. Argys, University of Colorado at Denver
Daniel I. Rees, University of Colorado at Denver

Using state-level variation in kindergarten start dates coupled with information on birth and interview dates to generate an exogenous measure of the relative age of a student’s peer group, we find that, controlling for age, females with older peers are more likely to use substances than females with younger peers. In contrast, there is little evidence that having older peers is related to the risky behavior of male adolescents. Because there is no reason to suspect that birth and kindergarten start dates should be correlated with the choice of school, the socioeconomic status of a child’s peers, or neighborhood unobservables, we view our results with regard to females as providing support for the idea that peer behavior can be contagious.