1. Department of Internal Medicine, Healthcare Research Institute, Healthcare System Gangnam Center, Seoul National University Hospital, Seoul, Korea.
2. Department of Internal Medicine, Seoul National University Bundang Hospital, Seongnam, Korea.
3. Department of Statistics and Actuarial Science, Soongsil University, Seoul, Korea.
4. Department of Medical Statistics, College of Medicine, The Catholic University of Korea, Seoul, Korea.
5. Division of Gastroenterology, Department of Internal Medicine, Yonsei University College of Medicine, Seoul, Korea.