Division of Gastroenterology;
Department of Internal Medicine;
University of Ulsan College of Medicine;
Asan Medical Center;
Seoul 138-736;
South Korea;
Department of Internal Medicine;
Inje University Ilsan Paik Hospital;
Koyang 411-706;
South Korea;
Department of Clinical Epidemiology and Biostatics;
University of Ulsan College of Medicine;
Asan Medical Center;
Seoul 138-736;
South Korea;