1. Musculoskeletal Research Unit, Bristol Medical School, University of Bristol, Bristol, UK
2. Biomedical Research Centre, National Institute for Health Research, University of Bristol, Bristol, UK
3. Oxford Trauma and Emergency Care, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK
4. Statistics and Epidemiology, Warwick Medical School, University of Warwich, Warwick, UK