1. Department of Child Health, University of Liverpool, Liverpool, UK
2. Alder Hey Children's Hospital, Liverpool, UK
3. Oxford Trauma and Emergency Care, Nuffield Department of Orthopaedics Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK
4. Oxford Clinical Trials Research Unit, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK
5. Department of Economics & Laboratory of Applied Economics, University of Western Macedonia - Kastoria, Kastoria, Greece
6. University of Liverpool, Liverpool, UK
7. University of Oxford Centre for Statistics in Medicine, Oxford, UK
8. University of Leicester, Leicester, UK
9. Warwick Medical School, University of Warwick, Coventry, UK