1. UCL Research Department of Epidemiology & Public Health, London WC1E 7HB, UK
2. MRC Unit for Lifelong Health and Ageing at UCL, London WC1E 7HB, UK
3. Population, Policy and Practice Research and Teaching Department, UCL Great Ormond Street Institute of Child Health, London WC1N 1EH, UK
4. CLOSER, Department of Social Science, UCL Institute of Education, London WC1H 0AL, UK
5. Musculoskeletal Science and Sports Medicine Research Centre, Department of Sport and Exercise Sciences, Faculty of Science and Engineering, Manchester Metropolitan University, Manchester M15 6BH, UK