Peer effects on student weight: randomization evidence from China

This paper investigates peer effects on student weight. Taking advantage of a national survey of middle schools in China, we exploit the BMI variation in randomly assigned classrooms. We find that having heavier peer classmates significantly increases a student's body weight. The results are consistent across various robustness checks based on a standardized measurement of BMI, alternative peer measures, a spurious correlation with height, and the validity of the instruments. Peer effects are more pronounced among female students, nonlocal students, rural students, and students with longer exposure to classmates. The quantile analysis suggests that the peer effect is stronger at the lower end of the BMI distribution. These findings confirm the presence of social multiplier effects in middle schools, which is helpful in establishing health policies for reducing student overweight.