1. Centre of Methods and Policy Application in the Social Sciences (COMPASS), University of Auckland, Private Bag 92019 Auckland 1142 New Zealand
2. Faculty of Public Health and Policy, London School of Health and Tropical Medicine, 218, 15‐17 Tavistock Place London WC1H 9SH UK
3. Social Science Research Unit, Department of Childhood, Families and Health, University College London, Institute of Education London WC1H 0AL UK
4. Department of Medical Statistics, London School of Health and Tropical Medicine London WC1E 7HT UK
5. General and Adolescent Paediatrics, Population, Policy & Practice Programme, Institute of Child Health, University College London WC1N 1EH UK
6. Institute of Child Health, University College London, 30 Guilford Street London WC1N 1EH UK