1. Department of Surgery and Cancer, South Kensington Campus, Imperial College London, London SW7 2AZ, UK
2. Department of Colorectal Surgery, Chelsea and Westminster NHS Foundation Trust, 369 Fulham Road, London SW10 9NH, UK
3. Laboratory of Hygiene, Social & Preventive Medicine and Medical Statistics, School of Medicine, Aristotle University of Thessaloniki, 541 24 Thessaloniki, Greece
4. Cochrane Methods Support Unit, Evidence Production and Methods Department, Cochrane, London W1G 0AN, UK
5. Department of Anesthesiology, State University of New York Downstate Health Sciences University, 450 Clarkson Avenue, Brooklyn, NY 11203, USA
6. Department of Colorectal Surgery and Cancer, The Royal Marsden NHS Foundation Trust, 203 Fulham Road, London SW3 6JJ, UK
7. Evangelismos General Hospital, Ipsilantou 45-47, 106 76 Athens, Greece