1. School of Public Health, Qingdao University, Qingdao 266071, China
2. Qingdao Municipality Center for Disease Control and Prevention, Qingdao 266033, China
3. Qingdao Institute of Preventive Medicine, Qingdao 266033, China
4. Department of Epidemiology and Biostatistics, School of Public Health, Peking University Health Science Center, Beijing 100191, China
5. Chinese Academy of Medical Sciences, Beijing 100730, China
6. Clinical Trial Service Unit and Epidemiological Studies Unit (CTSU), Nuffield Department of Population Health, University of Oxford, Oxford OX3 7LF, UK