How to assess and analyse session-specific effects and predictors: An example with the Metacognitive Training for Obsessive-Compulsive Disorder intervention.

It is essential to understand the effects of specific therapy elements (i.e., mechanisms of change) to optimize the efficacy of available treatments. There are, however, existing challenges in the assessment and analysis of constructs of interest. The present study aims to improve research on the effects of specific therapy elements using the example of the Metacognitive Training for Obsessive-Compulsive Disorder (MCT-OCD) intervention. Specifically, we introduce an innovative analytical method to identify predictors of treatment outcome and expand the assessment of common factors (e.g., coping expectations). A sample of 50 day- and inpatients with OCD was assessed before and after participation in an 8-week MCT-OCD programme. We investigated within-session change in scores on revised questionnaires administered before and after each session. Linear mixed models (for session-effects) and lasso regression (for prediction analyses) were used to analyse data. The revised assessments and data analyses showed greater improvement in dysfunctional (meta-)cognitive beliefs over the time of the intervention and within sessions compared to previous MCT-OCD studies. Some predictors, for example, improvement in coping expectation after the module on overestimation of threat for treatment outcome, were identified. The present study contributed to a better understanding of how to assess and analyse data of a modular intervention and demonstrated the strengths and weaknesses of different analytic approaches. Moreover, the analyses provided a deeper understanding of the specific effects and mechanisms of change of MCT-OCD modules, which can be refined and examined in future studies.