1 Centre for Surgical Research & MRC ConDuCT-II Hub for Trials Methodology Research, School of Social & Community Medicine, University of Bristol, Bristol, UK. [email protected].
2 Division of Surgery, Head & Neck, University Hospitals NHS Foundation Trust, Bristol, UK. [email protected].
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.