1. University Witten/Herdecke; Institute for Research in Operative Medicine (IFOM) - Department for Evidence-based Health Services Research; Ostmerheimer Str. 200 (Building 38) Cologne Germany 51109
2. HELIOS Klinikum Berlin-Buch and Faculty of Health - Witten/Herdecke University; Department of General, Visceral and Cancer Surgery; Schwanebecker Chaussee 50 Berlin Germany 13125