Interventions:
The selection of the comparators was appropriate and consistent with the scope of the analysis, which compared the periods before and after implantation for these patients. There was no clear description of the treatment given in the period before implantation.
Effectiveness/benefits:
The clinical analysis focused on the assessment of QALYs. Few patients were enrolled and this was the main limitation of the analysis, but this was a pilot study. The study was conducted in one centre and might not be representative other UK centres, as acknowledged by the authors. A randomised controlled trial was not possible for this type of intervention, mainly for ethical reasons. The EQ-5D was a valid instrument for the assessment of health-related quality of life, but it was noted that QALYs might lack sensitivity when comparing the efficacy of two similar drugs and in the treatment of less severe health conditions.
Costs:
Only those costs borne by or charged to the NHS were considered, in accordance with the perspective. The authors stated that general practitioner (GP) costs were not analysed because of a lack of reliable data; their inclusion would have increased the total costs in the pre-implantation period, making the IDDS more cost-effective. Not all the unit costs and resource quantities were presented separately, reducing the transparency of the analysis. Standard UK sources were used for the unit costs. Statistical analysis was conducted to compare the costs before and after IDDS implantation. Other details, such as the currency and price year, were reported.
Analysis and results:
The results were clearly presented and the costs and benefits were synthesised, using an appropriate incremental approach. The authors did not mention discounting and this would have been relevant for the long-term horizon of four years. The uncertainty was investigated using appropriate tests that focused on the small sample as the primary source of uncertainty. The results cannot be transferred to other settings, as acknowledged by the authors.
Concluding remarks:
Despite the small sample and some methodological weaknesses, this pilot study raised an interesting issue, in the importance of the latent period, and the authors’ conclusions appear to be valid.