“…Differences in the speed of return-to-work can be considered important, since the longer a worker is on sick leave, the more difficult it is to return to work (Hildebrandt et al 1997;Frank et al 1998;Verbeek 2001). It should be noted that return-towork does not always occur as a result of a patients' Effect size is small if d=0.2, medium if d=0.5 and large if d=0.8 (Cohen 1988(Cohen , 1992 health improvement (Pransky et al 2002;Van der Klink et al 2003). Complaints and functioning are, therefore, both relevant outcomes for the individual patients.…”