Effectiveness of Cognitive Analytic Therapy for Mixed Anxiety and Depression in the Context of Borderline Traits: A Quasi-Experimental Single Case Design Evaluation

The evidence base for the use of cognitive analytic therapy (CAT) as a short-term, integrative, and relational psychotherapy for anxiety and depression is building. This study contributes by intensively studying change in two types of quantitative outcomes (ideographic and nomothetic) over treatment time. The study employed an A/B quasi-experimental single case design method with a 15-year old male patient with a diagnosis of mixed anxiety and depression in the context of borderline personality disorder (BPD) traits. Following the 21-day baseline period (A), treatment was delivered over 77 days (B). Scores on three ideographic measures (self-worth, ability to connect with emotions, and interpersonal connection) were collected daily throughout. Two nomothetic outcome measures (CORE-OM and IIP-32) were collected at four time points, including a 6-week follow-up. The intervention was adherent to the CAT model and was competently delivered. Ideographically, CAT was shown to effectively enable better connection with emotions and with people and also improved self-worth. However, little change was observed on the two nomothetic outcomes measures. The study suggests that the CAT intervention was partially successful. The study is discussed in terms of the potential of integrating single race research methods into therapy provided for patients with common mental health problems underpinned by BPD traits. Methodological limitations and clinical implications are discussed.