4 - (OP5) Is Targeting Rumination the Pathway to CBT Success? An Examination of Data from the Skill Enhanced CBT Trial

Brooding, a facet of rumination, is a well-established risk factor for depression. In the revised treatment manual for CBT of depression (Beck et al., 2024), the authors posit that reduction in rumination is a central mechanism of change. However, empirical work testing this hypothesis is very limited. Clarifying the role of brooding in CBT for depression is essential for determining whether CBT outcomes differ based on the severity of ruminative tendencies and for evaluating the extent to which changes in rumination contribute to successful treatment.

We drew data from a trial of 150 adults with major depressive disorder who were randomly assigned to 12 weeks of either standard cognitive behavioral therapy (CBT) or a skill-enhanced adaptation (CBT-SE). Brooding was assessed pre and posttreatment using the Ruminative Responses Scale–Short Form, and depressive symptoms were measured with the Quick Inventory of Depressive Symptomatology–Self-Report during treatment and the Patient Health Questionnaire–9 over six-month follow-up. Using hierarchical linear models, we assessed baseline brooding and changes in brooding from pre to posttreatment in predicting the course of depressive symptoms during treatment. We examined brooding change and posttreatment brooding as predictors of cumulative depression symptom severity and risk of relapse over the follow-up period.

On average, patients experienced medium-sized reductions in brooding from pre to posttreatment (d = 0.55, p < .0001). After adjusting for baseline depression, baseline brooding did not predict the rate of change in depressive symptoms (or posttreatment depression severity). However, greater brooding reductions were concurrently associated with steeper declines in depression across treatments, even adjusting for baseline depression severity (β = 0.11, p = .0002). Moreover, greater brooding reductions (and lower posttreatment brooding) predicted lower cumulative depression severity over six-month follow-up (β = 0.29 and 0.24, p = .001 and .002, respectively). Only in analyses examining risk of relapse was there evidence of moderation by treatment condition. Specifically, greater brooding reductions (and lower posttreatment brooding) predicted reduced relapse risk in the CBT condition only (Hazard Ratio for standardized brooding = 1.88 and 1.80, p = .032 and .016, respectively). These effects were significant above and beyond depressive symptoms.

Overall, initial brooding severity showed limited prognostic value for treatment outcomes. Nonetheless, reductions in brooding during therapy emerged as an important marker of successful depression improvement and maintenance posttreatment. These findings align with theory conceptualizing rumination change as a possible mechanism of CBT, though it is important that further research clarify the temporal dynamics involved. Findings support the possibility that addressing brooding could be a pathway for maximizing the therapeutic impact of CBT for depression.