1. Department of Gastroenterology and Alimentary Tract Surgery, Tampere University Hospital, Teiskontie 35,33520 Tampere, Finland Department of Surgery, University of Turku,Turku, Finland
2. Department of Surgery, University of Turku, Turku, Finland Department of Digestive Surgery, Turku University Hospital, Turku, Finland
3. Department of Biostatistics, University of Turku, Turku, Finland