[1] Karolinska Inst, Inst Environm Med, Musculoskeletal & Sports Injury Epidemiol Ctr, SE-17177 Stockholm, Sweden
[2] Scandinavian Coll Naprapath Manual Med, Naprapathogskolan, SE-11419 Stockholm, Sweden
[3] Univ Toronto, Dalla Lana Sch Publ Hlth, Div Epidemiol, Toronto, ON, Canada
[4] Univ Ontario, Inst Technol, UOIT CMCC Ctr Disabil Prevent & Rehabil, Fac Hlth Sci, Oshawa, ON, Canada
[5] Univ Toronto, Inst Hlth Policy Management & Evaluat, Toronto, ON, Canada