1. Department of Family Medicine, Samsung Medical Center, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Seoul, Korea.
2. Department of Family Medicine, Korea University Ansan Hospital, Korea University College of Medicine, Ansan, Korea.
3. Department of Family Medicine, Inje University Busan Paik Hospital, Inje University College of Medicine, Busan, Korea.
4. Department of Epidemiology, School of Public Health, Seoul National University, Seoul, Korea.
5. Institute of Health and Environment, Seoul National University, Seoul, Korea.