Floor K Grote1
, Wilma Oostdijk1
, Sabine MPF De Muinck Keizer-Schrama2
, Paula van Dommelen3
, Stef van Buuren3,4
, Friedo W Dekker5
, Arnoldus G Ketel6
, Henriette A Moll2
and Jan M Wit1 
1Dept. of Paediatrics, Leiden University Medical Center, Leiden, The Netherlands
2Dept. of Paediatrics, Erasmus MC – Sophia Children's Hospital, Rotterdam, The Netherlands
3Dept. of Statistics, TNO Quality of life, Leiden, The Netherlands
4Dept. of Methodology & Statistics, University of Utrecht, The Netherlands
5Dept of Clinical Epidemiology, Leiden University Medical Center, Leiden, The Netherlands
6Dept. of Paediatrics, Spaarne Hospital, Haarlem, The Netherlands