Evidence of the idiographic effect of cognitive analytic therapy and analysis of its primary outcome measure

Cognitive analytic therapy (CAT) is a popular psychotherapy used by clinicians for a variety of mental health presentations. CAT has an emerging evidence base and a theoretically grounded outcome measure called the Personality Structure Questionnaire. A major aspect of the CAT evidence base consists of single-case experimental design (SCED) studies. As CAT adopts a non-manualised approach, then such studies are well-matched in terms of evaluations, as SCEDs are often utilised when interventions are tailored to individuals. SCEDs have unique methodological features including the presence of different study phases, with discrete baseline and intervention phases, and repeated measurement of problems of interest throughout. The target problem approach of CAT is therefore again well-matched to SCEDs, as target problems are measured by idiographic measures in single-case studies. Part I of this thesis is a systematic review exploring the effectiveness of CAT via the single-case evidence base. The results of 24 studies, including 26 patients, were identified and synthesised. Both published papers and studies available in the grey literature were reviewed. The quality of studies was assessed, with differences observed between published and unpublished studies. CAT was found to be effective for some diagnoses, but outcomes were less promising for other diagnoses such as anxiety and depression. Published studies were more likely to report effective CAT interventions; possible sources of bias are explored. Part II of this thesis is a network analysis of the Personality Structure Questionnaire (PSQ). The PSQ is an 8-item measure of identity disturbance and is central to assessment and outcome in CAT. A large sample (n = 1549) of secondary PSQ data was utilised to generate an overall network of identity disturbance and to compare networks of identity disturbance between the UK and Italy, adults and adolescents, clinical and community, and those with complex diagnoses and other diagnoses. There was a significant difference in networks of identity disturbance between the UK and Italy. No differences were identified in networks of identity disturbance between age, sample type or diagnosis. The results provide insight into identity disturbance and provide further evidence supporting the routine use of the PSQ in clinical settings. Together, these studies contribute to the evidence base for CAT and its primary outcome measure. The findings suggest that the effectiveness of CAT for patients’ target problems is dependent on their primary diagnosis and the qualification of the therapist. The networks of identity disturbance found allow clinicians using the PSQ to identify possible treatment targets for identity integration.