1. Musculoskeletal and Sports Injury Epidemiology Center, Institute of Intervention and Implementation Research , Karolinska Institute, IMM, Box 210 , 171 77 Stockholm , Sweden , Phone: +46-708-233 332
2. Unit of Health Care Sciences, Blekinge Institute of Technology , Karlskrona , Sweden
3. FoU Nordost Research and Development Unit Northeast Stockholm , Stockholm , Sweden
4. Musculoskeletal and Sports Injury Epidemiology Center, Sophiahemmet University , Stockholm , Sweden
5. Scandinavian College of Naprapathic Manual Medicine , Stockholm , Sweden
6. Karolinska Institute, Institute of Environmental Health , Stockholm , Sweden