1. Division of Gastroenterology, Department of Internal Medicine, Severance Hospital, Yonsei University College of Medicine , Seoul 03722 , Republic of Korea
2. Department of Health Policy and Management, Yonsei University Graduate School of Public Health , Seoul 03722 , Republic of Korea
3. Institute of Health Services Research, Yonsei University , Seoul 03722 , Republic of Korea
4. Department of Preventive Medicine, College of Medicine, Yonsei University , Seoul 03722 , Republic of Korea
5. Department of Biostatics, College of Medicine, Yonsei University , Seoul 03722 , Republic of Korea