Differential effect of early response on outcomes in person-centered experiential therapy and cognitive behavioral therapy for the treatment of adult moderate or severe depression.

To investigate if Sessions 1-4 Patient Health Questionnaire-9 (PHQ-9) scores are associated with treatment outcome and if there is a differential effect between person-centered experiential therapy (PCET) and cognitive behavioral therapy (CBT). A secondary data analysis of a prospectively registered and ethically approved pragmatic, noninferiority randomized controlled trial comparing PCET and CBT for the treatment of moderate or severe depression. Latent growth curve modeling was applied to data from 274 patients who received ≥ five sessions of therapy to investigate the association between change in Sessions 1-4 PHQ-9 scores on a binary end-of-treatment outcome (i.e., reliable and clinically significant improvement; RCSI) and on final-session PHQ-9 scores. Estimated power was 80%. Change in Sessions 1-4 PHQ-9 scores was significantly associated with the probability of RCSI in the PCET condition (p = .002) but not the CBT condition (p = .156). Specifically, greater early treatment improvement and higher PHQ-9 scores at Session 1 were significantly associated with obtaining RCSI in PCET, but not in CBT; this relationship differed significantly between conditions (p = .007). Greater early treatment improvement was also significantly associated with lower final-session PHQ-9 scores (p < .001), but this relationship did not significantly differ across conditions (p = .121). Early session scores are associated with final-session depression scores, though PCET and CBT manifest distinctively different trajectories for patients achieving RCSI. (PsycInfo Database Record (c) 2025 APA, all rights reserved).