1. Jangseong Public Health Center (D.S.), Jangseong, 515-800 South Korea
2. Department of Family Medicine (S.K.), Korea Cancer Center Hospital, Seoul 139-240, South Korea
3. Department of Family Medicine (K.H.K., S.M.P.), South Korea
4. Department of Family Medicine (K.L.), Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seongnam-si, Gyeonggi-do 463-707, South Korea
5. Department of Biomedical Sciences (S.M.P.), Seoul National University Hospital, Seoul National University College of Medicine, Seoul 110-744, South Korea