Case Formulation in Cognitive Behavioural Therapy for Psychosis

Abstract

This thesis explored case formulation (CF) in Cognitive Behavioural Therapy for psychosis (CBTp). CF is considered a key process in therapy. Chapter 1 introduces key definitions and outlines a range of psychological models used as the basis of a formulation. Chapter 2 provides a systematic review and narrative synthesis of the CF literature, focusing on the key question of whether formulations are reliable. Findings indicated a lack of consistency in how reliability is investigated, in part reflecting the wide range of models that may be used when formulating. To address this low rate of agreement, Chapter 3 demonstrates how a 3-stage Delphi method was used to establish international expert consensus for components of a CF in relation to auditory hallucinations, and persecutory delusions. Findings revealed that CFs should be parsimonious and focused on perpetuating (maintaining) factors to facilitate change. Chapter 4 uses methods of causal inference to examine whether CF modified treatment effects, for service users that received CBTp in a RCT. The findings provided a tentative signal that longitudinal CFs in CBTp may lead to poorer treatment effects, if explored too early on in therapy. In addition, a ‘dose-response’ was found, suggesting that length of therapy appears to be important. Using Reflexive Thematic Analysis, Chapter 5 explores the personal impact of CF from a service user perspective. Several themes were developed, including an overarching theme that considered the role of different levels of CF as a vehicle for change. Using mixed methods (systematic review, Delphi expert consensus, predictors of response to treatment, qualitative interviews with people with lived experience), the chapters in this thesis collectively highlight the importance of maintenance features in relation to the formulation of CBTp, but not in relation to outcome. Chapter 6 provides an overall discussion of the thesis findings.