1. HM Vermeulen, PhD, is Physical Therapist and Manual Therapist, Department of Physical Therapy, H0-Q, Leiden University Medical Center, PO Box 9600, 2300 RC Leiden, the Netherlands
2. PM Rozing, MD, PhD, is Professor of Orthopaedics, Department of Orthopaedics, Leiden University Medical Center
3. WR Obermann, MD, PhD, is Radiologist, Department of Radiology, Leiden University Medical Center
4. S le Cessie, PhD, is Statistician, Department of Medical Statistics, Leiden University Medical Center
5. TPM Vliet Vlieland, MD, PhD, is Epidemiologist, Departments of Physical Therapy and Rheumatology, Leiden University Medical Center