[1] Norwegian Inst Publ Hlth, Cluster Hlth Serv Res, POB 222 Skoyen, N-0213 Oslo, Norway
[2] Akershus Univ Hosp, Div Surg, N-1478 Oslo, Norway
[3] Univ Oslo, Inst Cliniacal Med, Problemveien 7, N-0315 Oslo, Norway
[4] Univ Hosp North Norway, Dept Qual & Res, Sykehusvegen 38, N-9019 Tromso, Norway
[5] Helgelandssykehuset, Dept Surg, Prestmarkveien 1, N-8800 Sandnessjoen, Norway