1. Centre for Clinical Brain Sciences, The University of Edinburgh, Edinburgh EH16 4SB, UK
2. Usher Institute, Centre for Population Health Sciences, The University of Edinburgh, Edinburgh EH8 9AG, UK
3. Department of Sociological Studies, The University of Sheffield, Sheffield, S10 2TU, UK
4. Directorate of Public Health and Health Policy, NHS Lothian, Waverley Gate, 2-4 Waterloo Place, Edinburgh EH1 3EG, UK