Social interactions and smoking: evidence using multiple student cohorts, instrumental variables, and school fixed effects.

In this paper, I use a social interactions framework to detect whether individual smoking decisions are influenced by classmate smoking decisions. There are several large challenges in addressing this question, including the endogeneity of school (and thus classmates) through residential location choices, 'third factors' such as school-level unobservables that influence individual and classmate choices simultaneously, and the difficulty of the identification of parameters in empirical models of social interactions. In order to address these issues, I use an instrumental variables/fixed effects methodology that compares students in different grades within the same high school who face a different set of classmates and classmates' decisions. Preferred specifications suggest that increasing the proportion of classmates who smoke by 10% will increase the likelihood an individual smokes by approximately 3 percentage points. I compare these results with previous findings that are unable to use school fixed effects and/or use potentially invalid instruments and find that the current results suggest smaller social interactions in adolescent smoking decisions than some previous work. Copyright (c) 2009 John Wiley & Sons, Ltd.