1 Centre for Primary Care and Public Health, Barts and the London School of Medicine and Dentistry, Yvonne Carter Building, 58 Turner St, London E1 2AB, Whitechapel, UK
2 East London NHS Foundation Trust, London E1 8DE, UK
3 Department of Computer Science, University of Warwick, Coventry CV4 7AL, UK
4 Department of Primary Care Health Sciences, University of Oxford, 2nd floor, New Radcliffe House, Walton St, Oxford OX2 6GG, UK