1. Centre for Surgical Research, School of Social and Community Medicine, University of Bristol, Bristol, UK
2. Division of Surgery, Head and Neck, University Hospitals Bristol NHS Foundation Trust, Bristol Royal Infirmary, Bristol, UK
3. Department of Surgery, University Hospitals of Leicester NHS Trust, Leicester Royal Infirmary, Leicester, UK
4. Department of Surgery and Cancer, Imperial College London, London, UK
5. National Institute for Health Research Pancreas Biomedical Research Unit, Royal Liverpool and Broadgreen University Hospital and University of Liverpool, Liverpool, UK
6. Centre for Statistics in Medicine, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK