1. Institute for Fiscal Studies , 7 Ridgmount Street, London WC1E 7AE, UK
2. Centre for Longitudinal Studies , UCL Social Research Institute, 20 Bedford Way, London, WC1H 0AL, UK and Institute for Fiscal Studies
3. Centre for Longitudinal Studies, UCL Social Research Institute , 20 Bedford Way, London, WC1H 0AL, UK and Institute for Fiscal Studies
4. University of Edinburgh Department of Psychology, , Edinburgh, UK