1. Department of Population Health, London School of Hygiene and Tropical Medicine , Keppel Street, London WC1E 7HT, UK
2. Population Health Sciences, Bristol Medical School, University of Bristol , Canynge Hall, Bristol BS8 2PS, UK
3. Division of Health Research, Lancaster University , Hazelrigg Lane, Lancaster LA1 4YW, UK
4. Mental Health Foundation , Long Lane, London SE1 4PD, UK
5. College of Medicine and Health, University of Exeter , Heavitree Road, Exeter EX1 2LU, UK
6. School of Health and Social Care, University of Essex , Wivenhoe Park, Colchester CO4 3SQ, UK