1. Department of Internal Medicine, College of Medicine, The Catholic University of Korea, Seoul, Korea.
2. Department of Internal Medicine, College of Medicine, Chung-Ang University, Seoul, Korea.
3. Department of Internal Medicine, College of Medicine, Yonsei University, Seoul, Korea.
4. Department of Internal Medicine, Kyung Hee University Medical Center, Seoul, Korea.
5. Department of Internal Medicine, College of Medicine, Soonchunhyang University, Bucheon, Korea.
6. Department of Pulmonary and Critical Care Medicine, Ajou University School of Medicine, Suwon, Korea.
7. Department of Internal Medicine, Eunpyeong St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea.
8. Department of Internal Medicine, College of Medicine, Ewha Womans University, Seoul, Korea.
9. Department of Applied Statistics, Chung-Ang University, Seoul, Korea.