1. Scandinavian Surgical Outcomes Research Group (SSORG), Department of Surgery, Sahlgrenska University Hospital/Östra, Gothenburg, Sweden
2. Department of Surgery, Alingsås Hospital, Alingsås, Sweden
3. Department of Surgery, Roskilde Hospital, Roskilde, Denmark
4. Department of Surgery, Herlev Hospital, University of Copenhagen, Copenhagen, Denmark
5. Department of Surgery, Caritas Clinic St Josef, Regensburg, Germany
6. VUmc University Medical Centre, Amsterdam, The Netherlands