Author: Priyadharshany Sandanapitchai
Sandanapitchai, Priyadharshany, 2025 Low-Intensity, High-Impact: A Randomized Controlled Trial of Online Guided Self-Help Cognitive Processing Therapy for PTSD , Flinders University, College of Education, Psychology and Social Work
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Using Cognitive Processing Therapy (CPT), this thesis examines approaches to addressing barriers to Posttraumatic Stress Disorder (PTSD) treatment, including cost, long waitlists, logistical difficulties, and stigma. It assesses the efficacy and practicability of adapting CPT into a guided self-help (GSH) format within a stepped care model to improve therapeutic efficiency and expand flexible treatment options. The main aims of this thesis were to assess the efficacy of stepped care and GSH in improving treatment outcomes, establish their non-inferiority to standard CPT, and evaluate the cost, acceptability, feasibility, and treatment moderators for GSH implementation.
Chapter 1 provided background context on PTSD, its broad impact, and outlined current treatment approaches and key implementation gaps. Two flexible models aimed at improving accessibility were introduced: the stepped care model, which matches the treatment intensity with the client’s needs and level of severity, and the GSH model, which offers structured, evidence-based content with minimal clinician support. Chapter 2 expanded on these concepts by conducting a systematic review and meta-analysis of structurally adapted CPT formats. Both the meta-analysis of randomized controlled trials (RCTs) and the review of non-RCT studies found no significant differences between adapted and standard CPT, providing a foundation for the next component of my thesis.
Guided by evidence supporting the CPT adaptations in Chapter 2, and given the need for scalable, resource-efficient trauma-focused treatments, Chapter 3 detailed the methodology for a RCT examining a novel adaptation of CPT in a GSH format within a stepped care model. This pilot study recruited 92 adults across Australia with full or subthreshold PTSD according to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) and randomized them into two conditions: the stepped care arm, where participants first enrolled in GSH and could be stepped up to standard CPT if needed, and the standard CPT arm, where participants directly received the standard CPT protocol via telehealth. The primary outcomes were PTSD, assessed through diagnostic status and symptom severity using the Clinician-Administered PTSD Scale (CAPS-5) and the PTSD Checklist (PCL-5); depressive symptoms, measured with the Depression, Anxiety and Stress Scale (DASS-21); and quality of life, assessed using the Assessment of Quality of Life 8-Dimensions (AQoL-8D). Outcome assessments for these measures were conducted at posttreatment, as well as at 3-month and 6-month follow-ups.
As summarized in Chapters 4 and 5, both approaches led to significant improvements in PTSD symptoms, depression, quality of life, and comorbid conditions. Non-inferiority to standard CPT was established for clinician-reported PTSD and depression measures. The GSH model was not only more cost-effective but also acceptable and feasible from both clinician and client perspectives. Moderator analysis revealed better outcomes for female participants and those with more clinician contact. Although age influenced treatment effects, it varied based on data treatment. In the GSH condition, participants improved regardless of baseline PTSD severity, with no major differences between those who completed GSH alone, stepped up to standard CPT, or dropped out.
In conclusion, my findings offer practical insight into how PTSD treatment can be delivered in a more scalable and accessible fashion through the GSH approach within a stepped care framework. By addressing current research and clinical gaps, and demonstrating that this approach is effective, cost-efficient, feasible, and acceptable, this study paves the way for further examination of GSH use in routine care. This study demonstrates that, although further research is needed to refine and expand these approaches, low-intensity, evidence-based models can deliver therapeutic benefits, increase reach, and reduce barriers to timely PTSD care.
Keywords: posttraumatic stress disorder (PTSD), cognitive processing therapy (CPT), treatment, adaptations, guided self-help
Subject: Psychology thesis
Thesis type: Higher Doctorate
Completed: 2025
School: College of Education, Psychology and Social Work
Supervisor: Reg Nixon