1. Department of Gastroenterology, Asan Medical Center, University of Ulsan College of Medicine, and Asan Digestive Disease Research Institute, Seoul, Korea
2. Department of Pathology, Asan Medical Center, University of Ulsan College of Medicine, and Asan Digestive Disease Research Institute, Seoul, Korea
3. Department of Clinical Epidemiology and Biostatistics, Asan Medical Center, University of Ulsan College of Medicine, and Asan Digestive Disease Research Institute, Seoul, Korea