1 Department of Special Needs, Education, and Youth Care, Faculty of Behavioural and Social Sciences, University of Groningen, Groningen, The Netherlands.
2 Dundee Centre for Health and Related Research, School of Nursing and Health Sciences, University of Dundee, Dundee, UK.
3 DeltaQuest Foundation, Inc., Concord, MA, USA.
4 Departments of Medicine and Orthopaedic Surgery, Tufts University School of Medicine, Boston, MA, USA.
5 Research Institute of Child Development and Education, Faculty of Social and Behavioural Sciences, University of Amsterdam, Amsterdam, The Netherlands. oort.qolr@uva.nl.