1. Department of Family Medicine and Primary Care, Faculty of Medicine, The University of Hong Kong, Hong Kong, China,
2. Department of Statistics and Actuarial Science, Run Run Shaw Building, The University of Hong Kong, Pokfulam Road, Hong Kong, Hong Kong, China and
3. Institute of Social Medicine and Family Medicine, School of Public Health, Zhejiang University, 866 Yuhang Tang Rd., 310058 Hangzhou, China