Minimum detectable effect size for main outcomes (accounting for sample
design and clustering)
The minimum detectable effect size (MDES) for the sample is calculated through using Optimal Design Software (Spybrooke et al., 2001). With 383 participants and individual randomization and without adding controls, the MDES is approximately 0.29 standard deviations for 80 % power and 95% confidence interval. If we assume that control variables explain 20% of the variation in the outcome variable (R^2 = 0,2 for control variables), this is reduced to 0.26.
For reference, a meta-analysis found that effect sizes of MCII (with written content) on various outcomes were within the confidence intervals of 0.15-0.39 of a pooled standard deviation for interventions (Wang et al, 2021).