Amit Kaura1, Jonathan A C Sterne2, Adam Trickey3, Jamil Mayet4. 1. National Institute for Health Research Imperial Biomedical Research Centre, Imperial College London and Imperial College Healthcare NHS Trust, London W2 1NY, UK. 2. National Institute for Health Research Bristol Biomedical Research Centre, University of Bristol and University Hospitals Bristol NHS Foundation Trust, Bristol, UK; Department of Population Health Sciences, University of Bristol, Bristol, UK. 3. Department of Population Health Sciences, University of Bristol, Bristol, UK. 4. National Institute for Health Research Imperial Biomedical Research Centre, Imperial College London and Imperial College Healthcare NHS Trust, London W2 1NY, UK. Electronic address: j.mayet@imperial.ac.uk.