Department of Surgery, Northwest Clinics, Alkmaar, the Netherlands. Electronic address: tvgestel@diakhuis.nl.Department of Surgery, Northwest Clinics, Alkmaar, the Netherlands.Department of Surgery, Amsterdam University Medical Center Location VU, Amsterdam, the Netherlands.Care and Public Health Research Institute, Maastricht University, Maastricht, the Netherlands.Department of Epidemiology, University Medical Center Groningen, Groningen, the Netherlands.Medical Library, Vrije Universiteit Amsterdam, Amsterdam, the Netherlands.South Tees Hospitals NHS Foundation Trust, UK; Honorary Professor, Hull York Medical School and Teesside University, UK.Department of Surgery, Amsterdam University Medical Center Location VU, Amsterdam, the Netherlands.Department of Surgery, Northwest Clinics, Alkmaar, the Netherlands.Department of Surgery, Northwest Clinics, Alkmaar, the Netherlands.