Sample size calculation
We expected a discontinuation rate of 15% for patients in the SPD condition and 40% for patients in the SPD + MBCT condition. To detect this difference with a power of 80%, alpha of 0.05 (two-sided), intraclass correlation of 0.05 due to cluster randomization, which was estimated to range between 0.00 and 0.05 in primary care in a previous study [