138 CHAPTER 6 caregivers’/patients’ wishes for follow-up treatment. Confidence intervals (CIs) and number needed to treat were reported when applicable. Number needed to treat indicates the number of patients needed for a specific treatment that results in one additional successful outcome. Student’s t-tests were applied to evaluate the time spent in the operation room. A generalized linear model was used to predict cost differences between BoNT-A and two-duct ligation. A Kolmogorov–Smirnoff test and Q–Q plots were used to analyse potential skewness of the cost distribution. On that basis, a gamma distribution and log link (relating the conditional mean cost to the covariates) was chosen for the generalized linear model. An ICER was calculated using the mean total cost differences and the treatment success after completing the trial. To assess the uncertainty in the ICER and identify the key cost drivers, we performed a sensitivity analysis for the duration of the surgical procedure in intervals of 5 minutes up to a minimum of 41 minutes. The sensitivity analysis included duration of the surgical procedure because the duration of two-duct ligation was dependent on the learning and/or teaching situation in the academic hospital. We did not performa sensitivity analysis for the loss of caregivers’ working hours because this is supposedly a direct effect of the invasiveness of the procedure. When patients crossed over to the other treatment arm, they were analysed according to the intention-to-treat principle. Patients who were excluded or who withdrew from the study were not included in the analyses. The power analyses showed that 26 patients per treatment arm were required to provide 80% power with 40% treatment success after BoNT-A and 80% treatment success after two-duct ligation to reveal a difference with a type 1 error rate of 5% wherein a 10% dropout rate was included.10 RESULTS Demographics Fifty-seven children were randomized to either two-duct ligation or BoNT-A. Four children withdrew from the study or were excluded from analyses. One other
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