Therapeutic Alliance, Treatment Intensity, and Symptom Change in Post-traumatic Stress Disorder: A Retrospective Study of Eye Movement Desensitization and Reprocessing-Centered Psychotherapy

Background Eye movement desensitization and reprocessing (EMDR)-centered psychotherapy is an evidence-based treatment for post-traumatic stress disorder (PTSD), yet symptom trajectories during routine outpatient care vary considerably. Process factors such as therapeutic alliance and treatment intensity may influence outcomes, but their independent and combined contributions in real-world clinical settings remain unclear. This study examined the relationships among therapeutic alliance, treatment intensity, and PTSD symptom change in a naturalistic outpatient context. Methods This single-center retrospective cohort study analyzed routinely collected clinical data from adults with a clinician-confirmed chart diagnosis of PTSD based on the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) criteria who completed EMDR-centered psychotherapy at a single outpatient psychological clinic in the Philippines between 2022 and 2025. PTSD symptoms were assessed using the PTSD Checklist for DSM-5 (PCL-5) at baseline, mid-therapy, and post-treatment. Therapeutic alliance was measured at mid-therapy using the five-item Agnew Relationship Measure-5 (ARM-5). Treatment intensity was defined as the total number of completed psychotherapy sessions. Linear regression and moderation analyses examined associations between alliance, treatment intensity, and symptom change, adjusting for age, sex, trauma type, and therapy type. Results The sample included 138 patients. Mean PTSD symptom scores decreased from 43.7 at baseline to 37.8 at mid-therapy and 30.0 at post-treatment. Therapeutic alliance did not predict early symptom change (baseline to mid-therapy; β = -0.01, p = 0.878) but significantly predicted overall symptom reduction (baseline to post-treatment; β = 0.61, p < 0.001; R² = 0.245) and late-phase improvement (mid-therapy to post-treatment; β = 0.62, p < 0.001; R² = 0.207). Treatment intensity significantly predicted symptom reduction from baseline to post-treatment (β = -0.21, p < 0.001; adjusted R² = 0.251) and from mid-therapy to post-treatment (β = -0.26, p < 0.001). Moderation analyses showed no significant interaction between therapeutic alliance and treatment intensity across treatment phases (all p > 0.10), indicating independent effects. Conclusions In routine outpatient EMDR-centered psychotherapy, therapeutic alliance and treatment intensity independently predict PTSD symptom improvement. Alliance appears most consequential after initial treatment engagement, while greater session completion supports sustained symptom reduction. These findings underscore the importance of fostering a strong working alliance beyond early sessions and promoting adequate treatment exposure to optimize outcomes in real-world trauma-focused care.