Individual Differences in Response to Once Versus Twice Weekly Sessions of CBT and IPT for Depression

Objective: The Personalized Advantage Index (PAI) is a method to guide treatment selection by investigating which of two or more treatments is optimal for a given individual. Recently, it was shown that, on average, twice-weekly sessions of psychotherapy for depression lead to better outcomes compared to once-weekly sessions. The present study applied the PAI method to assess if subgroups of patients may have a differential response to psychotherapy frequency. Method: Data came from a clinical trial (n = 200) randomizing depressed patients into different session frequencies: weekly sessions versus twice-weekly sessions. Machine-learning techniques were used to select pretreatment variables and develop a multivariable prediction model that calculated each patient's PAI. Differences in observed depression post-treatment scores (Beck Depression Inventory-II [BDI-II]) were tested between patients that received their PAI-indicated versus non-indicated session frequency. Between-group effect sizes (Cohen's d) were reported. Results: We identified prognostic indicators generally associated with lower post-treatment BDI-II regardless of treatment assignment. In addition, we identified specific demographic and psychometric features associated with differential response to weekly- versus twice-weekly therapy sessions. Observed post-treatment BDI-II scores were significantly different between individuals receiving the PAI-indicated versus non-indicated session frequency (d = .37). Conclusions: Although a higher session frequency is more effective on average, different session frequencies seem beneficial for different patients. Future studies should externally validate these findings before they can be generalized to other settings. What is the public health significance of this article? Although a higher session frequency is more effective for depression on average, different session frequencies might be beneficial for different patients. Results in the present sample indicated that a higher session frequency might be most beneficial for patients with less than two earlier treatments, low-reported happiness, males, with higher behavioral activation, lower physical functioning, better general health, a longer duration of symptoms considered as untenable, better perceived health change in the past year, and low-working memory. Furthermore, patients with more previous treatments, worse general health, higher working memory, and higher reported happiness may benefit more from the once-weekly sessions. These findings require external validation before they can be generalized to other settings.