Strengths and weaknesses of our investigations. The isolated labour force group

Our investigation was based on a consecutively collected patient group with no other selection than what was performed by the family doctors in their clinical practice and the guidelines from RTW and OPC. The control group was constructed to match this group. To be close to clinical practice can be recognized as strength. This relation was emphasised in the informational material distributed to the family doctors and NAV (section 1.1.3).

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The matching individuals in the study group and the control group became sick listed in the same month. Thus, the influence from the financial crisis was minimalized. That was a strength.

The lack of matching in both ethnicity and in occupational category would tend to give lower return to work rates in the study group than in the control group. As mentioned before (chapter 2.2.3), the inequality between the study and the control group was a challenge. This is further discussed in chapter 8.1.4 below.

Improving the method was done by reducing the study group and the control group to include only those who are in the work force full time—NAV Group 1 at t0. Both groups were still numerous as presented in chapter 4. They covered 62 % of the total study group and 80 % of total control group. Thanks to this, the study and control groups were expected to be as equal as possible from observation starting at t0, especially concerning work ability. In our study, diagnoses demonstrated no significant difference when focusing on RTW (Chapter 6).

This was recognized as an improvement of the method and a strength of the study.

When the differences between the study and control group for NAV Group 1 was significant from t₀ (chapter 3), the difference in the labour force group (chapter 4) was not significantly different on return to labour force before at t₁₂. From t₁₂ to t₃₆ the difference in return to workforce were best for the control group, p<0,001. The possible explanation of these differences is discussed below. If the study and the control group from the labour force were similar at t₀, the one-day intervention would be expected to initiate a difference during the first months. That effect was not observed. Instead we observed no development of a difference between the groups from labour force from t0 to t6 (Table 4.2). That could be an effect of the improvement of the method as the study group and control group had an equal development until t12.

The labour force, NAV Group 1 (Table 4.2), was redistributed and decreased significantly in the study group from 100 % at t0 to 34.7 % at t12 and 40.1 % at t36. For the control group, the numbers were 100 % at t0, 59.1 % at t12, and 55.8 % at t36, p<0,001. The one-day intervention seemed insufficient to make any difference the first half year, but a difference became visible from t12. That is an indication of little or no effect on RTW from the multidisciplinary brief intervention of one day. The difference developing between the study group and the control group from t12 must be due to factors other than the intervention.

Groups like NAV Group 1–5 have not been tested on a multidisciplinary intervention as a brief intervention before. The grouping of NAV categories is not used in other contexts outside NAV, but the grouping seems to be operational and demonstrates the changes in

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labour market and benefit status within the cohort during the follow-up period. This grouping specified the possibility to assess RTW and illustrate the transitions among NAV categories.

This method was recognized as useful and a strength when we were using data from an official register.

Øyeflaten et al. (106) used other categories and did not find that the probability of RTW was related to work or benefit status at departure from the rehabilitation clinic. Among the results were increased probability for working, a decreased probability for being on sick leave, and an increased probability for being on disability pension. The intervention was a work-related rehabilitation program and four years follow-up. She used official national register data. Our brief intervention was too short.

The transition from full-time to part-time sick leave was an announced official policy that the family doctors tried to implement, and it succeeded. In an assessment from 2013, Mykletun (11) argues that the number on full-time sick leave became lower and part-time sick leave increased, which reduced the total number of listed for a time. Employees sick-listed part time would be a workforce resource that could be used more if employers and society were able to access them. Nossen (18) concluded in 2014 that an increase in part-time sick leave also was followed by prolonged sick leaves. The overall effect on RTW was minimalized.

Our results confirmed a transition to part-time sick leave but did not confirm that our brief intervention with a multidisciplinary group improved the return to the labour force in the study group as compared with the control group. However, it may be argued that the brief intervention on the labour force group prevented and delayed the start of the negative development for the study group after t6. That was a strength. Individuals were then redistributed to the other NAV groups as will be focused on in section 8.3.

In our study, we found that from t6 to t36, there were significant differences between the study and control groups in all NAV categories. The control group had a higher

participation in the work force, a lower use of social benefits and a low degree of disability pension. That was not expected.

Our brief intervention program was based on earlier experiences from programs for patients with drug and alcohol problems, minor psychiatric complaints, fibromyalgia or other diffuse chronic pain conditions and low back pain (28, 44, 85, 113). The brief intervention has been found to be useful for both drug addicts (38) and for patients with anxiety/depression and fibromyalgia. Methods of approach were different, but closer personal contact, a

cognitive-oriented approach, physical exercises and examinations from the professionals in a

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reassuring atmosphere seemed to be favourable, as also mentioned by Braathen (85). This wide range of disorders from the musculoskeletal system and from minor mental disorders has not been investigated together in a multidisciplinary brief intervention before in the context of NAV groups.