1 Department of Epidemiology and Public Health, Sciensano, 1050 Brussels, Belgium; Department of Rehabilitation Sciences, Ghent University, Ghent, Belgium. Electronic address: robby.depauw@ugent.be.
2 EBPI-UWZH Musculoskeletal Epidemiology Research Group, University of Zurich and Balgrist University Hospital, Zurich, Switzerland; Epidemiology, Biostatistics and Prevention Institute (EBPI), University of Zurich, Zurich, Switzerland; University Spine Centre Zurich (UWZH), Balgrist University Hospital and University of Zurich, Zurich, Switzerland.
3 Department of Epidemiology and Public Health, Sciensano, 1050 Brussels, Belgium.