Searching for Peer Group Effects: A Test of the Contagion Hypothesis
利用出生日期和幼儿园入学日期构造同伴相对年龄的外生变量，发现女生同伴年龄较大时更易使用成瘾物质，支持同伴行为具有传染性。
Using information on birth and kindergarten start 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. 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. Copyright by the President and Fellows of Harvard College and the Massachusetts Institute of Technology.