1. Department of Epidemiology and Public Health, University College London , 1-19 Torrington Place, London WC1E 7HB, United Kingdom
2. Department of Social and Preventive Medicine, University of Malaya , Level 5, Block I, Kuala Lumpur 50603, Malaysia
3. Center for Health Policy Research and Evaluation, School of Public Administration and Policy, Renmin University of China , No. 59 Zhongguancun Street, Haidian District, Beijing 100872, China
4. Henan Province Yongcheng Central Hospital , Zhongyuan Road, Yongcheng, Shangqiu 476610, China