1. From Department of Rehabilitation Medicine (J.H.v.d.L., H.B.) and Institute for Research in Extramural Medicine (EMGO Institute) (J.H.v.d.L., H.B., D.L.K., H.C.W.d.V., L.M.B.), VU University Medical Center, Amsterdam, the Netherlands. Present affiliation for J.H.v.d.L.: Center for Pediatric Clinical Epidemiology, Academic Medical Center, Amsterdam, the Netherlands.