Social Comparisons and Adolescent Body Misperception: Evidence From School Entry Cutoffs

We provide novel evidence on the role of social comparisons in shaping adolescent body misperception. Using an instrumental variables approach leveraging variation in relative age generated by school entry cutoff months and data from the Health Behaviour in School-Aged Children study, we show that relatively younger students are more likely to describe their bodies as lighter than the clinically relevant BMI category implied by their reported heights and weights compared to their same-age counterparts who are relatively older within their respective classrooms. This result is driven by relatively younger students who are classified as normal weight for their age describing themselves as "too thin." We then show that relatively younger students are more likely to desire to gain weight, consume more calorie-dense foods, and report lower levels of physical activity. Overall, our results suggest that relatively younger students base their weight-related expectations and behaviors on their older peers.