1. Department of Clinical Epidemiology, Aarhus University Hospital , Denmark
2. Department of Surgery, Svendborg Hospital OUH , Denmark
3. Department of Surgery, Linköping University Hospital , Linköping , Sweden
4. Department of Biomedical and Clinical Sciences, Division of Surgery, Linköping University , Linköping , Sweden
5. Department of Surgery, Aarhus University Hospital , Aarhus , Denmark
6. Department of Surgery, Randers Regional Hospital , Randers , Denmark