BMC Public Health 2009, 9:140 http://www.biomedcentral.com/1471-2458/9/140 aimed at strengthening the problem-solving behaviour of both the patient and his supervisor. Measures Diagnostic interview We used the Mini-International Neuropsychiatric Inter- view (MINI plus; Dutch version 5.0.0.) as a diagnostic interview in order to include or exclude patients [36]. To include patients, the MINI was administered for the clas- sification of symptoms of major depression, dysthymia, panic disorder, agoraphobia, social phobia, simple pho- bia, obsessive-compulsive disorder, generalized anxiety disorder, hypochondria, and adjustment disorder accord- ing to Axis I of DSM IV. Other parts of the MINI were used to exclude patients. Psychometric properties of the MINI can be considered as good [37]. Primary outcome Sick leave Time until full return to work and the duration of sick leave were used as primary outcome parameters. The time until full RTW was calculated as the number of calendar days from the first day of sick leave to the first day of full return to work. The duration of sick leave was calculated as the number of hours of calendar days on sick leave from the first day of sick leave until full return to work, lasting at least 28 calendar days without partial or full relapse. Secondary outcomes Sick leave As secondary measures of sick leave, we calculated the time until partial return to work and the prevalence rate of partial and full return to work at 3, 6, 9, and 12 months' follow-up. The time until partial RTW was calculated in a similar way to how we calculated time to full RTW. The prevalence rate was calculated as the number of persons who (partially or fully) returned to work divided by the total number of persons in the intervention or control group at 3, 6, 9, and 12 months' follow-up. Distress, anxiety, depression, and somatization We measured distress and somatization symptoms by using the distress and somatization subscales of the Four- Dimensional Symptom Questionnaire (4DSQ) [38]. Anx- iety and depressive symptoms were measured by the anx- iety and depression subscales of the 4DSQ and the Hospital Anxiety and Depression Scale (HADS). The Four-Dimensional Symptom Questionnaire (4DSQ) is a Dutch self-report questionnaire that consists of 50 items distributed over 4 subscales. The distress subscale contains 16 items and the total score ranges from 0 to 32, the depression subscale contains 6 items and the total score ranges from 0 to 12, the anxiety subscale contains 12 items and the total score ranges from 0 to 24, and the somatization subscale contains 16 items and the total score ranges from 0 to 32. Higher scores indicate more dis- tress, depression, anxiety, or somatization. The 4DSQ appears to be a valid and reliable self-report questionnaire for primary care patients. The Cronbach's alpha for the 4 subscales ranged from 0.84 to 0.90 [38]. The Hospital Anxiety and Depression Scale (HADS) is a 14-item self-report screening scale. It contains two 7-item subscales for anxiety and depression. Both subscale scores range from 0 to 21 with higher scores indicating more depression or anxiety. The HADS showed good homoge- neity and reliability, with Cronbach's alpha for the sub- scales anxiety and depression ranged from 0.81 to 0.84 and from 0.79 to 0.86, respectively, in different Dutch samples [39]. Fatigue We measured fatigue by using the multi-dimensional Checklist Individual Strength Questionnaire (CIS). CIS consists of 20 statements distributed over four dimen- sions: subjective feeling of fatigue (8 items), motivation (4 items), physical activity (3 items), and concentration (5 items). Each item is scored for the past 2 weeks on a 7- point Likert scale ranging from 1 (true) to 7 (not true). The CIS was able to measure changes in fatigue scores in groups as well as in individual workers in randomized controlled trials [40]. Furthermore, the discriminant validity of the CIS was adequate for employees in occupa- tional groups [41]. The internal consistency of the CIS was also good for clinical and working populations, and the Cronbach's alpha for the total CIS was found to be 0.90 [42] and 0.91 [43], respectively. Work capacity We measured current work ability by using a single item of the Work Ability Index (WAI). We asked the patient to estimate their current work ability compared with their lifetime best. The score of this item ranges from 0 (cannot work at all) to 10 (best ever). The evidence for internal validity, predictive validity for disability, and test-retest reliability of the WAI questionnaire in workers was satis- factory [44,45]. Working conditions We measured working conditions by using 9 out of the 14 subscales of the VBBA core questionnaire: a self-report questionnaire on perception and judgement of work. We used the subscales work pace and workload (11 items), emotional strain (7 items), decision latitude (8 items), autonomy (11 items), social support colleagues (11 items) and social support supervisor (11 items), ruminat- ing (4 items), enjoyment of work (9 items), and job inse- curity (4 items). The Cronbach's alpha for these scales Page 7 of 11 (page number not for citation purposes)