Is Targeting Depression Sufficient to Alleviate Anxiety Comorbidity? Exploring Between-Individuals Heterogeneity in Within-Individuals Processes

The well-documented between-individuals correlation between anxiety and depression cannot address within-individuals questions, such as whether targeting depression subsequently alleviates anxiety comorbidity. Recent studies have demonstrated the importance of focusing on within-individuals processes to provide evidence-based guidelines to commonly encountered questions in clinical practice. This study examined the within-patient effect of reduction in depression on subsequent reduction in anxiety during a treatment targeting depression, as well as the potential variability in this effect between patients. Data from a randomized controlled trial of more than 3,220 observations nested within 100 patients treated for depression were used. Findings indicate that at the sample level, targeting depression reduced depression, which, in turn, predicted a subsequent reduction in anxiety. Although no qualitatively distinct subgroups emerged, quantitative differences between individuals were found. The pretreatment interplay between depression and anxiety explains heterogeneity between individuals. The findings have implications for personalizing depression treatment to address comorbidities.