Variation in effect of intervention studies in research on sickness absence

Correspondence: Hans Joergen Soegaard Forskningsenhed Vest, Center for Psykiatrisk Forskning, Gl Landevej 43, 7400 Herning, Denmark Tel +45 7847 4660 Fax +45 7847 4637 Email hans-joergen.soegaard@ps.rm.dk Background: Intervention studies in sickness absence research demonstrate a low effect and ambiguous results in reducing sickness absence and improving work status. The aim of this study was to determine if the effect of interventions is related to type of intervention, target population, inclusion criteria used, and impact of the scientific quality of the studies. Methods: Based on a structured review of 57 studies, short-term, medium-term, and longterm effects were analyzed with regard to the type of intervention, target population, inclusion criteria, and scientific quality of the studies. Results: The overall result was that the effect rate was low, ie, about 20% for short-term effect (up to 6 months) and medium-term effect (6–12 months), and 40% for long-term effect ($12 months). Interventions using stress reduction were most effective with regard to shortterm and medium-term effects, whereas collaborative care was most effective for long-term effects. The effects were related to the inclusion criteria and, to a minor degree, to the scientific quality of the studies. Conclusion: In the field of sickness absence research, more attention should be paid to the interrelationship between the types of interventions, target populations, and inclusion criteria for the studies. Larger studies of high methodological quality are needed. Steps should be taken to standardize outcome measures.