1. Department of Health Policy and Management, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
2. Stanford Center on China’s Economy and Institutions, Stanford University, Stanford, California, USA
3. Department of Health Behavior and Social Medicine, West China School of Public Health and West China Fourth Hospital, Sichuan University, Sichuan, China
4. Department of Pediatrics, Stanford University School of Medicine, Stanford, California, USA