1. Centre for Surgical Research, School of Social and Community Medicine, University of Bristol, Bristol, UK
2. Centre for Statistics in Medicine, Nuffield Department of Orthopedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK
3. Academic Department of Surgery, School of Cancer Sciences, Queen Elizabeth Hospital Birmingham, University of Birmingham, Birmingham, UK
4. Clinical Trials Evaluation Unit, School of Clinical Sciences, University of Bristol, Bristol, UK
5. Division of Surgery, Head & Neck, University Hospitals Bristol NHS Foundation Trust, Bristol, UK