1Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Canada
2Canadian Memorial Chiropractic College, Canada
3Department of Internal Medicine, German Hospital, Buenos Aires, Argentina
4Academic Medical Center, department of Orthopaedic Surgery, Meibergdreef 9, 1105 AZ, Amsterdam, the Netherlands
5School of Rehabilitation Sciences, McMaster University, Hamilton, Ontario, Canada
6Faculty of Kinesiology and Health Studies, University of Regina, Regina, Canada
7Ontario Chiropractic Association, Toronto, Ontario, Canada
8The Canadian Chiropractic Association, Toronto, Ontario, Canada
9Institute for Work and Health, Toronto, Ontario, Canada
10Division of Preventive Medicine and the Knowledge and Evaluation Research Unit, 200 First Street SW, 55905 Rochester, MN, USA