1 Department of Epidemiology and Biostatistics, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China; Department of Epidemiology and Biostatistics, West China School of Public Health, Sichuan University, Chengdu, China.
2 China Centre for Health Development Studies, Peking University, Beijing, China; Department of Global Health & Development, Faculty of Public Health & Policy, London School of Hygiene & Tropical Medicine, London, UK.
3 China Centre for Health Development Studies, Peking University, Beijing, China. Electronic address: qmeng@bjmu.edu.cn.