Comorbid anxiety symptoms predict lower odds of improvement in depression symptoms during smartphone-delivered psychotherapy

Comorbid anxiety disorders are common among patients with major depressive disorder (MDD), and numerous studies have identified an association between comorbid anxiety and resistance to pharmacological depression treatment. However, less is known regarding the effect of anxiety on non-pharmacological therapies for MDD. We apply machine learning techniques to analyze MDD treatment responses in a large-scale clinical trial (n=754), in which participants with MDD were recruited online and randomized to different smartphone-based depression treatments. We find that a baseline GAD-7 questionnaire score in the "moderate" to "severe" range (>10) predicts greatly reduced probability of responding to treatment across treatment groups. Our findings suggest that depressed individuals with comorbid anxiety face lower odds of substantial improvement in the context of smartphone-based therapeutic interventions for MDD. Our work highlights a simple methodology for identifying clinically useful "rules of thumb" in treatment response prediction using interpretable machine learning models and a forward variable selection process.