1. Department of Surgery, Kansai Medical University, Hirakata 573-1010, Japan
2. Department of Mathematics and Statistics in Medical Sciences, Kyoto Prefectural University of Medicine, Kyoto 606-0823, Japan
3. Department of Surgery, Meiwa Hospital, Nishinomiya 663-8186, Japan
4. Department of Gastroenterology and Hepatology, Kansai Medical University, Hirakata 573-1010, Japan