1. Department of Social and Environmental Health Research, London School of Hygiene and Tropical Medicine, London, UK
2. Centre of Methods and Policy Application in the Social Sciences, The University of Auckland, Auckland, New Zealand
3. School of Social Sciences, Cardiff University, Cardiff, UK
4. Department of Social Science, UCL Institute of Education, London, UK
5. Department of Medical Statistics, London School of Hygiene & Tropical Medicine, London, UK
6. UCL Institute of Child Health, London, UK
7. Warwick Medical School–Statistics and Epidemiology, University of Warwick, Coventry, UK
8. Department of Primary Care Health Sciences, University of Oxford, Oxford, UK