1. Clinical Trial Service Unit and Epidemiological Studies Unit, Nuffield Department of Population Health, University of Oxford, Richard Doll Building, Old Road Campus, Oxford OX3 7LF, UK
2. MRC Population Health Research Unit, Nuffield Department of Population Health, University of Oxford, Oxford, Old Road Campus, Oxford, OX3 7LF, UK
3. Department of Vascular Surgery, University Medical Center Utrecht, Utrecht University, Heidelberglaan 100, 3584 CX, Utrecht, The Netherlands
4. Nuffield Department of Primary Care Health Sciences, University of Oxford, Radcliffe Primary Care Building, Radcliffe Observatory Quarter, Woodstock Rd, Oxford OX2 6GG, UK
5. Nuffield Department of Surgical Sciences, John Radcliffe Hospital, Headley Way, Oxford OX3 9DU, UK