1. Department of Epidemiology (J.S.), School of Public Health and Institute of Health and Environment, Seoul National University, Seoul 151-742, Korea
2. Department of Family Medicine (K.L.), Busan Paik Hospital, Inje University College of Medicine, Busan 614-735, Korea
3. Department of Family Medicine (Y.-M.S.), Samsung Medical Center, and Center for Clinical Research, Samsung Biomedical Research Institute, SungKyunKwan University School of Medicine, Seoul 135-710, Korea