1. Research Department of Primary Care and Population Health, University College London, Royal Free Campus, London NW3 2PF, UK
2. Population Health Sciences Institute, Newcastle University, Newcastle upon Tyne NE2 4AX, UK
3. British Heart Foundation Glasgow Cardiovascular Research Centre, Institute of Cardiovascular and Medical Science, University of Glasgow, Glasgow G12 8TA, UK
4. Population Health Research Institute, St George's, University of London, London SW17 0RE, UK