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

Objective: To investigate if session 1–4 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).

Methods: A secondary data analysis of a prospectively registered and ethically approved pragmatic, non-inferiority randomized controlled trial comparing PCET and CBT for the treatment of moderate or severe depression. Latent Growth Curve Modelling was applied to data from 274 patients who received ≥ five sessions of therapy to investigate the association between change in session 1–4 Patient Health Questionnaire (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%.

Results: Change in session 1–4 PHQ-9 scores were 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).

Conclusions: Early session scores are associated with final-session depression scores, though PCET and CBT manifest distinctively different trajectories for patients achieving RCSI.

Public health significance statement: Routine outcome monitoring may be essential to detect early signs of patient-therapy misfit by session 4 in PCET as a process-marker for reviewing and possibly increasing process-guiding interventions that provides clearer structuring during therapy. In CBT specifically, reviewing at session 4 may help reduce the potential for patients dropping out, although early response may provide less of a cue to later outcomes for more severe patients.