Association for Public Policy Analysis & Management

Understanding the causal impacts of peer effects and social networks is important for designing policies that can leverage social multipliers to maximize effectiveness and reduce obesity rates. Social and peer influence have been shown to amplify the effects of genetic factors, environmental traits, and policy interventions across multiple risky health behaviors in children and adolescents, but less is known about the effects of peers on weight outcomes.

This paper uses a within-school, across-cohort empirical design to estimate the causal effects of peer obesity on individual health outcomes across critical developmental periods in childhood, using a unique and detailed longitudinal dataset of New York City public school children. We find that increases in the average Body Mass Index (BMI) composition of a child's cohort increases that child's own BMI, even after adjusting for individual-level sociodemographics, school environments, time trends and school-specific time trends. Results are heterogeneous by gender, race/ethnicity, and grade level, suggesting that there is a developmental gradient and the effects of peers decline as children age. Evidence from extensive balancing tests and robustness checks support the exogeneity of our identification strategy.

The results from this study can be used to directly test for the existence of social multiplier effects in the evaluation of existing school wellness policies, as well as heterogeneous multiplier effects in sub-group analyses. Analyses of peer effects and successful interventions can potentially show how policy can impact children who are not directly treated by a program/intervention (social spillover), and how the heterogeneity of social effects (developmentally and across demographic groups) can be leveraged to plan better programs/interventions.