Strengths and limitations
The main strength of this study is that we compared app-based treatment with care-as-usual. The pragmatic design is considered the gold standard for economic evaluations in health care.24 Other strengths are the inclusion of all common UI types, the use of patient-centred and validated outcome measures, the 12-month follow-up period, and the inclusion of sensitivity analyses to confirm the robustness of our data.
The cost and effect analyses were sufficient to make valid conclusions about cost-effectiveness. Although the ICER and ICUR are typically used to represent costs associated with 1 unit of health gain, we set the difference to focus on cost rather than health gains given that the latter was comparable between the groups. Consideration of this health gain would be confusing, as the minimal differences result in high ratios of ICER and ICUR.
Limitations that must be considered are power and loss to follow-up. Often, cost-effectiveness studies are underpowered because their power depends on the primary outcome measure of a trial. This trial was powered on non-inferiority of effectiveness after 4 months. In this secondary analysis, 172 women (65.6%) were available for follow-up and power was lower. By performing a bootstrap analysis, this issue does not affect the results of the cost-effectiveness analysis. However, the lower power must be considered in our effectiveness and subgroup analyses. Loss to follow-up was associated with higher body mass index. Participation of these women could have further improved effects and lowered costs for both treatment groups, as weight loss is effective for UI and a cheap intervention.