1. Erasmus Medical Center; Department of General Practice; PO Box 2040 Rotterdam Netherlands 3000 CA
2. VU University Medical Center; Department of Clinical Epidemiology; PO Box 7057 Amsterdam Netherlands 1007 MB
3. Universidade Estadual de Londrina; Laboratory of Biomechanics and Clinical Epidemiology, PAIFIT Research Group; Av. Robert Koch 60 Londrina Parana Brazil 86038-350
4. Katholieke Universiteit Leuven, Tervuursevest; Faculty of Kinesiology and Rehabilitation Sciences; 101 Leuven Belgium 3001
5. Maastricht University; Department of Epidemiology; P.O. Box 616 Maastricht Netherlands 6200 MD
6. VU University; Department of Epidemiology and Biostatistics, EMGO Institute for Health and Care Research; PO Box 7057 Amsterdam Netherlands 1007 MB