1. Section for Preventive Medicine and Epidemiology, Institute of Health and Society, University of Oslo, Oslo, Norway.
2. Tibet University Medical College, Lhasa, Xizang, People's Republic of China.
3. National Institute of Public Health, Oslo, Norway.
4. Epidemiology Unit, Prince of Songkla University, Songkhla, Thailand.
5. Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway.