Exploring mechanisms of change in two sequential studies evaluating the metacognitive training for depression using lasso regression

The Metacognitive Training for Depression (D-MCT) is a highly structured group therapy that has been shown to be effective in reducing depressive symptoms. First evidence suggests that need for control represents a mechanism of change. However, more research is needed to evaluate the mode of action of each module and identify predictors of treatment response. Two sequential studies (one naturalistic pilot study [study I, N = 45] and one randomized controlled trial [study II, N = 32]) were conducted to evaluate the session-specific effects and predictors of D-MCT in patients with depression. The D-MCT was conducted over eight weeks, and patients answered a questionnaire on dysfunctional beliefs (e.g., negative filter) and depressive symptoms (e.g., lack of energy, self-esteem) before and after each session. Linear mixed-effects models showed that several dysfunctional beliefs and symptoms improved over the course of the treatment; three modules were able to evoke within-session effects, but no between-session effects were found. The improvement in lack of energy in one module was identified as a relevant predictor in study I via lasso regression but was not replicated in study II. Exploratory analyses revealed further predictors that warrant replication in future studies. The identified predictors were inconclusive when the two studies were compared, which may be explained by the different instruments administered. Even so, the results may be used to revise questionnaires and improve the intervention.