Sample size calculation

Given an estimated prevalence of 6% for PIU, we estimate a screening of 24 000 participants and a sample of 1440 participants eligible for the study. Assuming that the participation rate is around 60%, 864 participants could be enrolled in the study. With random assignment of 860 individuals to the intervention or control group, this sample size would ensure that a small effect (d=0.20) could be identified with a power of 80% and a 5% probability of error with two-sided testing for differences in means with a nonparametric test. Thus, a target size of 430 participants per group will be established. Approximately 250 participants are expected for the subsequent brief telephone intervention and 120 for the online therapy.