1. Department of Family Medicine and Primary Care, The University of Hong Kong, P.R. China
2. JC School of Public Health and Primary Care, The Chinese University of Hong Kong, P.R. China
3. The Institute of Social and Family Medicine, Zhejiang University School of Medicine, Hangzhou, P.R. China
4. Department of Statistics and Actuarial Science, The University of Hong Kong, P.R. China
5. International Diagnostic Centre, Clinical Research Department, London School of Hygiene & Tropical Medicine, UK
6. The Second Affiliated Hospital, Zhejiang University School of Medicine, Zhejiang University, Hangzhou, P.R.China