(PS3-77) Is CBT for Depression Inherently Transdiagnostic?

There is concern about how single-disorder protocols can best serve individuals with comorbidities. In the context of CBT for depression, the studies that have examined the effect of comorbid anxiety on treatment outcomes have found that intake anxiety predicts a greater rate of response in depressive symptoms (Forand et al., 2011) or at least an early rapid response (Forand et al., 2013). To further examine the effect of comorbid anxiety, we utilized self-report symptom data from a recent clinical trial of 150 adults with depression participating in CBT or skill-enhanced CBT, using the Quick Inventory of Depressive Symptomatology (QIDS-SR, Rush et al., 2003) and the Generalized Anxiety Disorder -7 scale (GAD-7, Spitzer et al., 2006). The average level of anxiety at baseline in the sample was moderate with considerable variation (M = 12.9; SD = 4.8). Utilizing random intercept cross-lagged panel modeling (RI-CLPM; Hamaker et al., 2015), we found that over the first 8 sessions, a hypothesized mechanism of change in CBT (cognitive change, as measured by the Cognitive Change-Sustained scale, Schmidt et al., 2019) significantly predicted within-person changes at the next session in depressive and anxious symptoms with relationships that were very similar in magnitude (β = -.27 and β = -.24, respectively). Hierarchical linear modeling analyses showed that baseline anxiety significantly predicted a steeper slope of change in depressive symptoms over the course of treatment (β = -.13). Additionally, we found the inverse relationship: baseline depression predicted a steeper slope of change in anxious symptoms throughout treatment (β = -.15). These relationships did not differ by condition. We used means and standard deviations from a general adult sample (Bailey & Strunk, 2023) as normative data. Clinical criteria for an elevated score was more than 0.5 standard deviations above the normative sample mean, whereas remission was defined as 0.5 standard deviations or less below the normative sample mean (Norman et al., 2003; Dunn et al., 2020). Among the 86% who met clinical criteria for elevated baseline depression using QIDS scores, 75% of them achieved remission based on endpoint QIDS scores. Among the 56% that met clinical criteria for baseline anxiety based on GAD-7 scores, 75% of them achieved remission based on endpoint GAD-7 scores. Taken together, these results are consistent with the hypothesized change mechanism of sustained cognitive change in CBT exerting a similar impact on both depressive and anxious symptoms within-person early in treatment. In addition, symptom severity, meaning either anxiety or depressive symptoms, predicts increased rates of response in the other kind of symptom throughout. We take our results to suggest that CBT for depression may have a transdiagnostic impact that has been under appreciated.