1. Department of Surgery, Orbis Medical Centre, Sittard
2. Department of Statistics, Maastricht University, Maastricht
3. Department of Surgery, Maxima Medical Centre, Eindhoven
4. Department of Internal Medicine, Academic Medical Centre, Amsterdam
5. Department of Epidemiology, Maastricht University, Maastricht
6. Department of Surgery, Catharina Hospital, Eindhoven, The Netherlands