1. Division of Gastroenterology and Hepatology, Stanford University Medical Center, Palo Alto, California, USA;
2. Division of Gastroenterology and Hepatology, Department of Internal Medicine, Hallym University Dongtan Sacred Heart Hospital, Hwaseong, Gyeonggi, South Korea;
3. Department of Epidemiology and Population Health, Stanford University School of Medicine, Palo Alto, California, USA.