1. Department of Pediatrics, West China Second University Hospital, Key Laboratory of Obstetric and Gynecologic and Pediatric Diseases and Birth Defects of Ministry of Education, Sichuan University, Chengdu, China
2. Evidence-Based Social Science Research Center, School of Public Health, Lanzhou University, Lanzhou, China
3. Department of Social Medicine and Health Management, School of Public Health, Lanzhou University, Lanzhou, China