Jane M Blazeby1,2, Paula R Williamson3, Doug Altman4. 1. Centre for Surgical Research & MRC ConDuCT-II Hub for Trials Methodology Research, School of Social & Community Medicine, University of Bristol, Bristol, UK. j.m.blazeby@bris.ac.uk. 2. Division of Surgery, Head & Neck, University Hospitals NHS Foundation Trust, Bristol, UK. j.m.blazeby@bris.ac.uk. 3. MRC North West Hub for Trials Methodology Research, Department of Biostatistics, University of Liverpool, Liverpool, UK. 4. Centre for Statistics in Medicine, Nuffield Department of Orthopaedics, Rheumatology & Musculoskeletal Sciences, University of Oxford, Oxford, UK.