1. Hepato-Biliary-Pancreatic Surgery Division, Department of Surgery, Graduate School of Medicine, University of Tokyo, Tokyo, Japan
2. Department of Health Economics and Epidemiology Research, School of Public Health, University of Tokyo, Tokyo, Japan
3. Department of Clinical Data Management and Research, Clinical Research Centre, National Hospital Organization Headquarters, Tokyo Medical and Dental University, Tokyo, Japan
4. Department of Health Care Informatics, Tokyo Medical and Dental University, Tokyo, Japan