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