Design and sample size
SAD
We conducted a simulation-based a priori power analysis for a 3 × 2 interaction (group ( time) in a linear mixed model for the primary outcome of SAD symptom severity (according to the LSAS), using the R package “simr” [We chose these effect sizes as conservative estimates based on the results of a recent meta-analysis reporting moderate effect sizes in ICBTs for SAD [We based our power analysis on an iterative simulation of increasing sample sizes with starting values of Study flowchartAs a robustness check, we additionally conducted a power analysis based on the simulation of a 3 × 3 interaction (group × time) that included the estimated effect sizes at 