1 Division of Epidemiology, School of Public Health and Primary Care, the Chinese University of Hong Kong, Hong Kong, China.
2 Department of Epidemiology and Biostatistics, School of Public Health, Peking University.
3 Chinese Academy of Medical Sciences.
4 Department of Epidemiology and Biostatistics, School of Public Health, Peking University. Chinese Academy of Medical Sciences. Email: lmlee@pumc.edu.cn.