1. Division of Paediatric Surgery, Department of Surgery, University of Groningen, University Medical Centre Groningen, Groningen, the Netherlands
2. Department of Paediatric Surgery, Emma Children's Hospital, Academic Medical Centre and VU University Medical Centre, Amsterdam, the Netherlands
3. Centre of Research on Psychology in Somatic Diseases, Tilburg University, Tilburg, the Netherlands
4. Department of Paediatric Surgery, Erasmus Medical Centre, Sophia Children's Hospital, Rotterdam, the Netherlands
5. Department of Paediatric Surgery, Wilhelmina Children's Hospital, University Medical Centre Utrecht, Utrecht, the Netherlands
6. Division of Paediatric Surgery, Department of Surgery, Radboudumc–Amalia Children's Hospital, Nijmegen, the Netherlands
7. Department of Paediatric Surgery, University Medical Centre Maastricht, University of Maastricht, Maastricht, the Netherlands
8. Anorectal Physiology Laboratory, Department of Surgery, University of Groningen, University Medical Centre Groningen, Groningen, the Netherlands