1 University of Cambridge, Department of Public Health and Primary Care, Forvie Site, Robinson Way, Cambridge Biomedical Campus, Cambridge, Cambridgeshire, UK, CB2 0SR.
2 Garswood Surgery, Station Road, Garswood, St. Helens, Merseyside, UK, WND 0SD.
3 Peking University, Institute of Population Research, Yiheyuanroad 5, Haidian District, Beijing, China, 100871.
4 University of Liverpool, Health Inequalities and the Social Determinants of Health, Liverpool, UK, L69 3GB.