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.