Sample size and statistical analysis
MDD, anxiety disorder, ABM
We estimated Baseline characteristics of participants in the two treatment groups were reported using frequency distributions and descriptive statistics including measures of central tendency and dispersion. The primary analysis was conducted using an intention-to-treat approach and included all randomized participants who had either baseline and/or follow-up data (For BDI-II and BAI, the model included condition (ABM, sham training) and assessment point (baseline, post ABM, six-months follow-up) and condition by time interaction as fixed factors. Due to the different intervals between assessment points, we treat time as a categorical variable. The same specifications were used for the analysis of BSRI and AB but included two time points only (baseline and post ABM). The model was fit using restricted maximum likelihood using the lme4 package in R (Bates, Mächler, Bolker, & Walker, If a Condition × Assessment point interaction effect [or in the case of predictor analyses (ongoing MDD or comorbid anxiety disorder): Predictor × Condition × Assessment point] was significant, pairwise analysis was used for decomposing the interaction effect. In case of an effect of ABM, we investigated whether state rumination and change in state rumination mediated the effect.At baseline, 15 participants had missing data on BDI-II, AB, and BAI and 14 participants had missing BSRI data. Participants with missing data at baseline, except for one who had follow-up data, were not included in the analysis. Missing data on follow-ups had the following distribution at various timepoints; BDI-II post-intervention: ABM All analyses were conducted using SPSS (version 27) and R (version 4.2.0).