J H Kim1, M C M Leung2, B H Yip3, X Su3, S M Griffiths3. 1. The School of Public Health 4/F, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong Special Administrative Region. Electronic address: jekim@post.harvard.edu. 2. The Department of Economics, 9th Floor, Esther Lee Building, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong Special Administrative Region. 3. The School of Public Health 4/F, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong Special Administrative Region.