1 Vascular Surgery Research Group, Imperial College London, Charing Cross Hospital, London W6 8RP, UK. Electronic address: j.powell@imperial.ac.uk.
2 Vascular Surgery Research Group, Imperial College London, Charing Cross Hospital, London W6 8RP, UK.
3 Cardiovascular Epidemiology Unit, Department of Public Health and Primary Care, University of Cambridge, Cambridge, UK.
4 Vascular Surgery Research Group, Imperial College London, Charing Cross Hospital, London W6 8RP, UK; Clinic for Vascular Surgery, Kantonsspital St Gallen, St Gallen, Switzerland.