1. MRC Social and Public Health Sciences Unit, University of Glasgow, Glasgow
2. Department of Psychology, University of Edinburgh, Edinburgh
3. Department of Epidemiology and Public Health, University College London, London
4. National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark
5. Department of Psychiatry and Behavioral Sciences, Duke University Medical Center, Durham, North Carolina, USA and MRC Epidemiology Resource Centre, University of Southampton, Southampton, UK