Outcomes
Treatment effectiveness after 12 months was assessed by the change in incontinence symptom severity scores, measured by the International Consultation on Incontinence Modular Questionnaire Urinary Incontinence Short Form (ICIQ-UI-SF), the condition-specific quality of life (ICIQ-LUTSqol), and the five-level version of the EuroQol health status measure (EQ-5D-5L).15-17 The minimum important differences for the change of score within the treatment groups have been established at 2.52 (SD2.56) for the ICIQ-UI-SF and 3.71 (SD 4.69) for the ICIQ-LUTSqol.18 A minimum important difference for the EQ-5D-5L was previously established at 0.04 amongst adults with type 2 diabetes.19
Costs were measured at a patient level at both 4 and 12 months based on enquiries about medical and non-medical consumption and productivity over the past 4 months. We used the adapted iMCQ and iPCQ questionnaires from the institute of Medical Technology Assessment and included the costs of app development and maintenance. We doubled the costs measured at 12 months to estimate costs between 4 and 12 months. We rated cost components collected during the trial based on the standard Dutch guideline for economic evaluations composed by the Dutch National Health Care Institute.21 The sum of costs was recorded as the total societal cost. All costs are presented in euros based on the 2017 year-end prices (2014 prices indexed to inflation by 2.414%). Yearly costs for app development and maintenance were based on the actual costs. A scenario of 30,000 users was used, derived as a conservative estimate from the number of users of freely available apps for UI and on the number of downloads of the Swedish Tät app.22
For the cost analysis, effectiveness was measured with the Incontinence Impact Adjusted Life Years (IIALY) score derived from the ICIQ-UI-SF symptom score.20 The IIALY score reflects disease-specific quality of life weighted from the patient’s perspective with a score from 0 (severe impact of UI on quality of life) to 1 (no impact of UI on quality of life). Utility was based on the EQ-5D-5L, with valuations generated using the Dutch tariff for the EQ-5D.17 The EQ-5D questionnaire is a generic quality of life questionnaire that generates preference-based scores from -0.33 (severe problems on all five dimensions) to 1 (best possible health state). Areas under the receiver operating characteristic curve were used to calculate the IIALYs and QALYs gained for each individual during the 12-month follow-up period: to gain one IIALY or one QALY at a population level (i.e. to add one additional life year in perfect health), the calculated amount (in euros) would need to be invested.