Discussion
O-ACT, insomnia
I-MORE had economic benefits over O-ACT, as shown by both the cost-effectiveness, and cost-benefit approach. While intervention costs were considerably higher for I-MORE, other healthcare costs and production losses were lower when compared to O-ACT. I-MORE led to 43 fewer days of sickness absence in a 24-month perspective, even when sickness absence during the intervention period, which was inevitably higher for I-MORE, was included. Thus, when estimating the ICER, I-MORE led to an additional cost of 278 euros per additional day a patient was at work. Since 278 is less than the average wage in Norway, which was 339 euros in 2016, this resulted in a net societal benefit of 2,667 euros, in favour of I-MORE.This is the first study performing a health economic evaluation on inpatient occupational rehabilitation in Norway. There are also few studies investigating comparable interventions internationally, especially in long-term and societal perspectives [I-MORE was considerably more expensive than O-ACT. Intervention costs for I-MORE was calculated as standard program costs per patient according to planned duration, the mix of individual and group-based activities, and according to an annual capacity. This approach was chosen since the program to a large extent was fixed and it was not considered feasible to directly observe time spent by therapists on individual patients over time. We used budget information as basis for costs, which in a Norwegian public hospital setting can be regarded as highly representative of actual expenditures. A similar method was used for O-ACT-costs, where a conservative approach was taken since no rents were included. When the results still suggest I-MORE was economically beneficial it is due to the high costs associated with production loss in O-ACT – or the benefit of more working days in I-MORE. It follows that a less conservative approach, and a potentially higher O-ACT cost will increase the economic benefits of I-MORE. Partly or graded sick leave was compiled into number of full days of sick leave in order not to overestimate the costs related to production loss [A substantial amount of the costs was due to the inpatient setting, meaning the intervention probably could be run at lower costs. Whether the effect of I-MORE would have been similar if it had been run as an outpatient program is an open question, but no such facilities currently exist in Norway. Advantages with an inpatient setting is that it offers a break from everyday life and an opportunity to focus on one`s own process, with regular meals and rest organized by the centre. Although overall beneficial in societal terms, providing a 3.5-week inpatient program to all potential users would potentially lead to large budget impacts on the healthcare sector. In a recent paper we found indications that I-MORE was particularly effective for individuals with insomnia [The main strengths of this paper were the randomized design and the use of registry data for both healthcare use and sickness absence. All Norwegian citizens are registered in these registries, ensuring no missing data and no recall bias. A limitation was that production loss was based on days on sick leave without considerations of reduced productivity when at work (i.e., presenteeism). Another limitation is the lack of cost-utility analyses which we were not able to include due to a considerable amount of missing data on health-related quality of life at all measurement points. The problem of missing data is a general problem in the evaluation of RTW-programs; future studies of the cost-utility of these types of interventions are therefore warranted. Also, the effect might also vary between subgroups, like for example different diagnoses groups or educational groups, but the sample size was insufficient for subgroup analyses. In this study we used a societal perspective, where the effect was measured as absence from work/ RTW and production costs. While the findings are relevant in settings where a societal perspective is appreciated, it might not form the basis for prioritization in settings where a healthcare perspective is used.