Peer effects in adolescent bodyweight: evidence from rural China.

Peer effect is a potential determinant of individual weight gain that has drawn considerable attention recently. The presence of peer effect implies that policies targeted at changing bodyweight can have enhanced effectiveness through a multiplier effect. This study aims to measure the peer effects on adolescent bodyweight in China. Using the small community nature of the rural sample of the wave 2000 of the China Health and Nutrition Survey, we define plausible peer groups and assess the effect of the average BMI of his/her peer group on the BMI of an adolescent. An instrumental variable (IV) approach is applied to control for potential endogeneity of the peer group's BMI. We find evidence supporting peer effect on BMI in general. The peer effect is around 0.3 with slight variation between two alternative peer definitions. Split sample analysis shows that the peer effect is significant for females (0.32-0.37), and insignificant for male adolescents. Furthermore, we find strong influence of same-gender peers (0.34-0.42) for female adolescents. Conditional quantile regressions show that the peer effect in weight gain is mainly present at or below the median in the conditional BMI distribution for girls, and at the higher end of the BMI distribution for boys. Multiple tests show strong identification, and strong instruments in our IV estimation. Placebo tests suggest that our results are reasonably robust to the correlated effect, due to unobserved community- and province-level factors.