1 Clinical Trial Service Unit and Epidemiological Studies Unit, Nuffield Department of Population Health, University of Oxford, Oxford, OX37LF, UK.
2 Medical Research Council Population Health Research Unit, Nuffield Department of Population Health, University of Oxford, Oxford, OX37LF, UK; Clinical Trial Service Unit and Epidemiological Studies Unit, Nuffield Department of Population Health, University of Oxford, Oxford, OX37LF, UK.
3 Health Economics Research Centre, Nuffield Department of Population Health, University of Oxford, Oxford, OX37LF, UK.
4 Medical Research Council Population Health Research Unit, Nuffield Department of Population Health, University of Oxford, Oxford, OX37LF, UK; Clinical Trial Service Unit and Epidemiological Studies Unit, Nuffield Department of Population Health, University of Oxford, Oxford, OX37LF, UK. Electronic address: colin.baigent@ndph.ox.ac.uk.