1. Department of Clinical Oncology; Tuen Mun Hospital, New Territories West Cluster; Hong Kong P. R. China
2. Department of Non-Communicable Disease and Cancer Epidemiology; Biomedical Research Institute of Granada, University of Granada; 18002 Granada Spain
3. Department of Non-Communicable Disease and Epidemiology; London School of Hygiene and Tropical Medicine; London WC1E 6HW UK
4. Department of Epidemiology; Harvard School of Public Health; Boston MA 02115 USA