1. Department of Surgery; Leiden University Medical Center; Leiden The Netherlands
2. Department of Surgery; Groene Hart Ziekenhuis; Gouda The Netherlands
3. Westfriesgasthuis; Hoorn The Netherlands
4. Department of Medical Statistics and Bioinformatics; Leiden University Medical Center; Leiden The Netherlands
5. Leiden University Mathematical Institute; Leiden The Netherlands
6. Performation; Bilthoven The Netherlands
7. XIS; Delft The Netherlands
8. Dutch Institute for Clinical Auditing; Leiden The Netherlands
9. Department of Surgery; Netherlands Cancer Institute-Antoni van Leeuwenhoek Hospital; Amsterdam The Netherlands