1 Statistics and Epidemiology Unit, Warwick Medical School, University of Warwick, Coventry, UK.
2 Sir Charles Gairdner Hospital and The University of Western Australia, Nedlands, Perth, Australia.
3 Oxford Clinical Trials Research Unit, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK.
4 Oxford Trauma, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK.
5 Department of Trauma and Orthopaedic Surgery, Centre for Clinical Research, Unfallkrankenhaus Berlin, Berlin, Germany.