1 Division of Population Medicine, School of Medicine, Cardiff University, Cardiff CF14 4YS, Wales, UK. Electronic address: GobatNH@cardiff.ac.uk.
2 Primary Care, Nuffield Department of Primary Care Health Sciences, Medical School Division, Oxford University, Radcliffe Observatory Quarter, Woodstock Rd, Oxford, England OX2 6GG, UK. Electronic address: christopher.butler@phc.ox.ac.uk.
3 School of Population and Global Health, University of Western Australia (M413), 35 Stirling Highway, Crawley, WA 6009, Australia. Electronic address: Steve.webb@uwa.edu.au.
4 Critical Care, HRB Funded Irish Critical Care-Clinical Research Core, University College Dublin School of Medicine, Department of Critical Care, St Vincent's University Hospital, Elm Park, Dublin 4, Ireland. Electronic address: alistair.nichol@ucd.ie.