1. Surgical Epidemiology, Trials and Outcome Centre (SETOC); St Mark's Hospital and Academic Institute; Harrow, Middlesex UK
2. Department of Surgery and Cancer; Imperial College London; London UK
3. Department of Molecular Medicine and Surgery; Karolinska Institutet; Stockholm Sweden
4. Center for Digestive Disease; Division of Coloproctology; Karolinska University Hospital; Stockholm Sweden
5. Academic Department of Surgery; University of Birmingham; Birmingham UK
6. Clinical Epidemiology Unit; Department of Medicine; Karolinska Institutet; Stockholm Sweden
7. Sachs' Children and Youth Hospital; Stockholm Sweden
8. Unit of Biostatistics; Institute of Environmental Medicine; Karolinska Institutet; Stockholm Sweden
9. Division of Surgery; Department of Clinical and Experimental Medicine; Faculty of Health Sciences; Linköping University; Linköping Sweden
10. Department of Surgery; County Council of Östergötland; Linköping Sweden