Understanding and predicting relapse of depression and anxiety following psychological interventions delivered in routine services

The Improving Access to Psychological Therapies programme (IAPT) in England enables a large population of people with depression and anxiety to receive evidence-based psychological treatments. The programme has been demonstrated to be effective in the short-term. However, the long-term outcomes of IAPT treatments are under-researched, despite it being well-established that depression and anxiety are highly recurrent disorders, and that relapse is relatively common following psychological interventions. Consequently, this thesis sought to contribute to the field’s understanding of relapse following psychological interventions delivered in routine practice, by aiming to improve our ability to predict its occurrence, and to assess its impact on patients and services. To begin, a systematic review (Chapter 2) of predictors of relapse of anxiety-related disorders following cognitive behavioural therapy (CBT) was conducted. An overall pooled relapse rate of 21.8% was estimated, and residual symptoms was identified as the only consistently supported risk factor of relapse. Two studies are then discussed (Chapters 3 and 4) in which a machine learning approach was implemented to predict relapse following low-intensity (LI) and high-intensity (HI) psychological interventions, with the developed models displaying promising predictive potential (AUC = 0.70-0.83). Following this, a qualitative study (Chapter 5) identified psychosocial factors, and in particular work-related stress, as being risk factors for symptomatic deterioration following LI interventions. This study also raised methodological issues regarding current approaches that are used to assess relapse occurrence. The last empirical study in this thesis (Chapter 6) examined the consequences of relapse from a health services perspective, with it being estimated that 13.7% of patients who receive treatment within IAPT subsequently return for additional treatment. Finally, Chapter 7 concludes the thesis by drawing together and synthesising the findings across the thesis, discussing their theoretical implications, and providing recommendations for clinical research and future research.