Table 2 The six studies meeting the quality criteria according to Straus et al9
 Study Participants employees at start of study? Participants work disabled because of MI or cLBP at start of study? Follow-up ⩾1 year? Loss to follow-up ⩽20% Adjustment for other prognostic factors? Justification for used set of prognostic factors? Total Froom et al 199910 Yes Yes Yes Yes Yes Yes 6 Boudrez and de Backer 200011 Yes Yes Yes Yes Yes Yes 6 Hansson and Hannsson 200012 Yes Yes Yes Yes Yes Yes 6 Van der Giezen et al 200013 Yes Yes Yes Yes Yes Yes 6 Nielsen et al 200414 Yes Yes Yes Yes Yes Not mentioned 5 Hamalainen et al 200415 Yes Yes Yes Not mentioned Yes Yes 5