BMC Public Health 2009, 9:140 http://www.biomedcentral.com/1471-2458/9/140 Background Common mental disorders and the effectiveness of interventions Common mental disorders (CMDs) are described as mild to moderately severe mental disorders. However, there is no generally accepted definition. Some experts define CMDs as consisting of depressive, anxiety, and somato- form disorders based on DSM IV criteria [1]. Others define CMDs as having a depressive episode or one of four differ- ent anxiety disorders defined by ICD-10, including mixed anxiety and depressive disorder with sub-threshold symp- toms [2], or define CMDs as ranging from stress symp- toms, measured by for instance the General Health Questionnaire, to minor usually mixed anxiety and depressive symptoms as often seen in primary care [3]. We defined CMDs as a broad concept including stress-related disorders and depressive, anxiety, and adjustment disor- ders based on DSM IV criteria. The working population prevalence rates of anxiety, depressive disorders, and stress-related disorders are high. Sanderson et al. [4] showed in a review that the working population prevalence rates vary by region. They found prevalence rates of depressive disorders varying from 2.2% in Australia to 4.8% in the Netherlands. Also, the prevalence rates of various anxiety disorders vary, such as from 0.1% in Australia to 1.8% in the US for agoraphobia, and from 5.2% in the US to 5.6% in the Netherlands for simple phobia. The prevalence rates of stress-related disor- ders, measured by the General Health Questionnaire (GHQ) or Maslach Burnout Inventory (MBI-GS) vary from 35% in the UK [3] to 27% in Finland [5]. The impact of CMDs on personal lives, companies, and society is substantial. CMDs are associated with personal costs such as a reduction in the quality of life, role func- tioning, and income. Furthermore, CMDs are associated with increased sick leave [2-5] and loss of productivity [4,6]. At a societal level, the estimated costs due to CMDs are deemed to be substantial. The annual costs of depres- sive disorders in the United States were estimated at $83.1 billion in 2000 [7]. A major proportion (62%) of these costs is due to loss of productivity, sickness absence, and work disability. Although there is a lack of cost-of-illness data related to anxiety disorders in Europe [8], some esti- mates are available from individual countries. The annual excess costs of prevalent cases of mood and anxiety disor- ders at population level in the Netherlands are estimated at 560 million euros [9] per 1 million people aged 18 to 65 years. Of these costs, 85% are due to production loss. Evaluation studies of clinical treatments for various anxi- ety and depressive disorders, such as cognitive behav- ioural therapy (CBT) and pharmacotherapy, showed that symptoms can be reduced effectively [10-13]. However, only a limited number of studies measured work-related outcomes [14] and hardly any studies demonstrated effec- tiveness in terms of reduced sick leave or increased pro- ductivity. We may therefore conclude that well-known evidence-based treatments for depressive and anxiety dis- orders such as CBT and medication can be effective in reducing symptoms but do not automatically reduce absenteeism or improve productivity. In order to achieve earlier return to work and build up productivity, work- directed interventions seem promising, especially when work conditions can be considered as causal factors. Van der Klink et al. [15] and Schene et al. [16] both con- ducted a randomized controlled trial (RCT) to evaluate the effectiveness of a work-directed intervention pro- gramme with workers on sick leave due to stress-related and major depressive disorders, respectively. They com- pared the intervention programme with care as usual. In both studies, they found a reduced duration of sick leave of a work-directed intervention programme. The mean duration of sick leave was reduced by 21 [15] and 92 days [16], respectively. Moreover, Blonk et al. [17] found, in a RCT on the effectiveness of an similar work-directed inter- vention programme for self-employed workers, a reduced median duration of sick leave of approximately 200 days, compared with a no treatment and a regular CBT control group. Furthermore, studies on the effectiveness of similar but not work-directed intervention programmes [18,19] showed no reduction of the duration of sick leave. So, there are indications that work-directed interventions can reduce sick leave more effectively. The above-described work-directed interventions [15-17] combined an activating problem-solving approach to per- ceived stressors and restoring contact with the working environment. These ingredients appear to contribute to a shorter duration of sick leave. For the activating problem- solving approach, this presumption is supported by the findings of Van Rhenen et al. [20]. They found, in a large cohort study of employees with a high stress level, that employees with an active problem-solving coping strategy are less likely to drop out because of sickness absence in terms of frequency, length, and duration of sickness absence. Moreover, an avoidant coping style was associ- ated with increased frequency of reporting sickness and the duration of sick leave. Restoring contact with the working environment by a gradual increase in working hours could be another effec- tive ingredient of work-directed intervention programmes that contributes to a shorter duration of sick leave, as the studies described above [15-17] also have this element in common. In order to increase working hours gradually during the return to work process and prevent avoidance of perceived stressors simultaneously, exposure in vivo as Page 2 of 11 (page number not for citation purposes)