[1] St Marys Hosp, Dept Vasc Surg, London W2, England
[2] Kensington & Chelsea & Westminster Hlth Author, Dept Publ Hlth, London, England
[3] Univ Sheffield, Sch Hlth & Related Res, Sheffield, S Yorkshire, England
[4] Imperial Coll Sch Med, Dept Epidemiol & Publ Hlth, London, England
[5] Royal Bournemouth Hosp, Dept Vasc Surg, Dorset, England
[6] Norfolk & Norwich Hosp, Dept Vasc Surg, Norwich, Norfolk, England