[1] Univ Wales Coll Med, Dept Surg, Cardiff CF4 4XN, S Glam, Wales
[2] Univ Wales Coll Med, Dept Epidemiol Stat & Publ Hlth, Cardiff CF4 4XN, S Glam, Wales
[3] Gen Infirm, Dept Surg, Leeds LS1 3EX, W Yorkshire, England
[4] Royal Surrey Cty Hosp, Dept Surg, Guildford, Surrey, England
[5] Queen Alexandra Hosp, Dept Surg, Portsmouth, Hants, England
[6] Derby City Gen Hosp, Dept Surg, Derby, England
[7] St James Hosp, Dept Surg, Leeds LS9 7TF, W Yorkshire, England