“…Ten papers were from a single centre studies, 10,12,13,22,23,25,26,28,32,37 nine were multi‐centre studies 3,5–7,14–17,27,29 and 17 were whole country studies 1,2,4,18–21,24,30,31,33–36 . Twenty‐five studies were retrospective 1,2,4–7,10,12,13,15,18–21,24–27,30,32–37 and nine prospective 3,14,16,17,22,23,28,29,31 . Studies ranged in size from 58 to 75 280 patients with a mean number of 13 189 patients per study.…”