Treating co-occurring depression and anxiety: Modeling the dynamics of psychopathology and psychotherapy using the time-varying effect model

Objective: We demonstrate the utility of the time-varying effect model (TVEM) for the analysis of psychotherapy data, with the aim of elucidating complex patterns of change over time and dynamic associations between constructs of interest. Specifically, we examine the association between depression and co-occurring anxiety in a sample of adults treated with interpersonal psychotherapy (IPT) for depression or a variant designed to address both depression and co-occurring anxiety (IPT-PS, IPT for depression with panic and anxiety symptoms). Method: Seventy-eight (82% female) adult outpatients with major depression and co-occurring anxiety were assessed at each of 16 outpatient treatment sessions using the Hamilton rating scales for depression and anxiety. Results: On average, depressive symptoms declined in a quadratic form over the course of treatment. While the association between anxiety and depression was modest early in treatment, it strengthened over the middle and latter treatment phases. Finally, exploratory analyses suggest that while IPT and IPT-PS were similarly effective in reducing depressive symptoms, IPT-PS may be more effective at uncoupling the association between core anxiety and depressive symptoms. Conclusions: Findings point to the utility of the TVEM for psychotherapy research and the importance of assessing anxiety in the course of treating depression, especially following the initial phase of treatment (i.e., after Session 5).