1. K. Verkerk, PT, MSc, Rotterdam University of Applied Sciences, Rotterdam, the Netherlands; Spine & Joint Centre, Rotterdam, the Netherlands; Department of General Practice, Erasmus MC, University Medical Center, Rotterdam, the Netherlands. Mailing address: Museumpark 40, 3015 CX Rotterdam, the Netherlands.
2. P.A.J. Luijsterburg, PhD, Department of General Practice, Erasmus MC, University Medical Center.
3. H.S. Miedema, MD, Rotterdam University of Applied Sciences.
4. A. Pool-Goudzwaard, PhD, Department of Neuroscience, Erasmus MC, University Medical Center, Rotterdam.
5. B.W. Koes, PhD, Department of General Practice, Erasmus MC, University Medical Center.