Politics & Governance / Public Policy / Healthcare Policy

Your Classmates Are Making You Fat? Shocking Evidence from Korea's Random Classroom Assignment

Jaegeum Lim, Jonathan Meer

Think your weight is just about your own choices? Think again. This video unpacks a groundbreaking study from South Korea that used random classroom assignments to prove something startling: your peers' BMI directly impacts yours. We dive into the data from 3,909 middle school students, showing how a one-unit increase in classmates' average BMI boosts your own by 0.83 units—and raises your risk of being overweight by 10.8 percentage points. But here's the twist: traditional statistics would tell you the opposite. We reveal the hidden biases, the surprising persistence of peer effects, and why this matters for public health. Authors Jaegeum Lim and Jonathan Meer from the National Bureau of Economic Research (NBER Working Paper 23901) show that interventions targeting obesity could have ripple effects through social networks. Watch to uncover the truth about social contagion in health.