1. J.C.E. Kempen, PhD, Department of Rehabilitation Medicine, VU University Medical Center, PO Box 7057, 1007 MB Amsterdam, the Netherlands; EMGO Institute for Health and Care Research, VU University and VU University Medical Center; and MS Center, Amsterdam, the Netherlands.
2. C.A.M. Doorenbosch, PhD, Department of Rehabilitation Medicine, VU University Medical Center; Research Institute MOVE, VU University and VU University Medical Center; and Academy of Human Kinetic Technology, The Hague University of Applied Sciences, The Hague, the Netherlands.
3. D.L. Knol, PhD, Department of Epidemiology and Biostatistics, VU University Medical Center.
4. V. de Groot, MD, PhD, Department of Rehabilitation Medicine, VU University Medical Center; EMGO Institute for Health and Care Research, VU University and VU University Medical Center; and MS Center.
5. H. Beckerman, PhD, Department of Rehabilitation Medicine, VU University Medical Center; EMGO Institute for Health and Care Research, VU University and VU University Medical Center; and MS Center.