Statistical Analysis
SECONDARY
For the cost-effectiveness analysis we calculated an incremental cost-effectiveness ratio (ICER) by dividing the difference in the mean costs (total health care costs) by the difference in mean number of working days during 24 months of follow-up:To avoid double counting, production loss was not included in the costs here since workdays was the effect measure (and production costs were estimated using the number of sick leave days). In the cost benefit analysis, the net societal benefit was calculated by subtracting the incremental costs (difference in total health care costs between the interventions) from the incremental benefit (difference in loss of production costs between the interventions).For both the cost-effectiveness and the cost-benefit analyses, uncertainty was assessed using bootstrapping techniques with 1,000 repetitions. The results from the bootstraps were displayed in a cost effectiveness plane. Using the bootstrapped results, we also estimated the 95% confidence bounds as the 2.5 and 97.5 percentiles of the 1,000 bootstrapped replications.Between group differences in total healthcare costs and for primary and secondary care were tested separately using generalized linear models with a log link and a gamma distribution [All analyses followed intention to treat principles. A prospectively agreed analysis plan was not written, but the economic analyses were described in the published protocol [