1. Division of Gastroenterology Department of Internal Medicine Dankook University Hospital Dankook University College of Medicine CheonanSouth Korea
2. Division of Gastroenterology Department of Internal Medicine Asan Medical Center University of Ulsan College of Medicine Seoul South Korea
3. Division of Gastroenterology and Hepatology Department of Medicine University of Maryland School of Medicine Baltimore USA
4. Department of Clinical Epidemiology and Biostatistics Asan Medical Center University of Ulsan College of Medicine Seoul South Korea