1. Department of Social Work, The Chinese University of Hong Kong, Hong Kong, China
2. Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, New York, USA
3. Department of Social Work & Social Administration, Sau Po Centre on Ageing, The University of Hong Kong, Hong Kong, China
4. Departments of Political Science and Statistics, and School of Education, Iowa State University, Ames, Iowa, USA