Hendriks E1, Kessels A G1, de Vet H C2, Bernards A T3, de Bie R1
1. Department of Epidemiology - Maastricht University - The Netherlands, 2. EMGO Institute, VU University Medical Center, Amsterdam, The Netherlands, 3. Department of Research and Development, Dutch Institute for Allied Health Care (NPi), Amersfoort, The Netherlands