Optimising depression interventions for young people and parents: a systematic review of factors associated with dropout and engagement in Group CBT for children and adolescents; and a mixed-methods evaluation of parent treatment optimisation

Wilcock, Matthew 2025. Optimising depression interventions for young people and parents: a systematic review of factors associated with dropout and engagement in Group CBT for children and adolescents; and a mixed-methods evaluation of parent treatment optimisation. ClinPsy Thesis, Cardiff University. Item availability restricted.

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Abstract

Depression is a common and often disabling condition that affects people across the lifespan. Psychological interventions, such as cognitive-behavioural therapy (CBT), are among the most effective tools we have to support recovery. However, not everyone benefits equally, and some people disengage before completing treatment. There is a growing need to understand how to make psychological interventions more effective, more engaging, and more responsive to individual needs. This thesis investigates how outcomes from psychological interventions for depression can be improved by identifying the factors that predict engagement and treatment response. It includes two studies. The first is a systematic review and meta-analysis that examines why some young people disengage from group-based CBT. The second is an empirical study exploring changes in depression symptoms among adults receiving a novel intervention, and what practitioners believe helps or hinders progress. Together, these studies aim to support the design and delivery of more effective psychological treatments by understanding how they are experienced and who they work best for. The first paper presents a systematic review of engagement and dropout in group CBT for depression in children and adolescents. Group CBT is widely used in this population because it is cost-effective and allows for shared learning between peers. However, group formats also introduce challenges, particularly around engagement. Some young people disengage early, which can limit the impact of therapy and reduce its overall effectiveness. The review examined 18 randomised controlled trials of group CBT for depression. It aimed to identify whether specific features of the intervention - such as the inclusion of behavioural activation, the involvement of parents, or the level of therapist training - were associated with dropout. It also explored whether characteristics of the sample, such as age or gender, were related to engagement. On average, dropout rates were relatively low, and no consistent differences were found between group CBT and comparison conditions. Analysis suggested that behavioural activation might be linked to lower dropout, but this finding was tentative. The review also highlighted major gaps in the literature: few studies clearly defined engagement, and most did not measure treatment satisfaction or the therapeutic relationship. These omissions limit the ability to identify what supports meaningful participation in therapy. The second paper is a mixed-methods evaluation of the Parent Treatment Optimisation (PTO) intervention, a psychological support programme for adults with depression. PTO was delivered as part of the wider SWELL trial and involved 12 weeks of tailored support including medication changes, access to online CBT and fortnightly check-ins with a clinician. The aim of this study was to understand how depressive symptoms changed over time during PTO, and whether certain baseline characteristics could predict those changes. Depression symptoms were measured every two weeks using a standard questionnaire. Statistical analysis showed that, on average, participants experienced a steady and clinically meaningful reduction in symptoms over the course of the programme. Lower income and a history of mental health difficulties were associated with more severe symptoms at the outset, but these factors did not influence the rate of improvement over time. To complement these findings, the study also included interviews with six practitioners who delivered PTO. Practitioners described a range of factors that helped or hindered engagement. Practical barriers, such as housing or financial stress, often interfered with participation. However, the flexibility of remote delivery - including video and phone calls - was viewed as a major facilitator of engagement. Practitioners also emphasised the importance of emotional connection and continuity - having someone regularly check in and ask how the person was doing - as a key ingredient in helping people make progress. Together, the two studies in this thesis highlight the importance of understanding not just whether psychological interventions for depression work, but how and for whom. The systematic review points to a lack of consistent reporting and measurement in trials of group CBT for young people, making it difficult to identify what promotes engagement. The empirical study suggests that psychological support can lead to meaningful improvements in adults with depression, and that flexibility, relational support, and practical relevance are likely to play important roles in that process. Across both papers, this thesis argues that improving psychological interventions is not just a question of content, but also of context. Understanding the predictors of engagement and outcome - and integrating these insights into intervention design - can help ensure that psychological therapies are not only effective, but also accessible and acceptable to those who need them most.

Item Type:	Thesis (DClinPsy)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Psychology
Subjects:	B Philosophy. Psychology. Religion > BF Psychology
Date of First Compliant Deposit:	26 August 2025
Last Modified:	15 Sep 2025 09:07
URI:	https://orca.cardiff.ac.uk/id/eprint/180635

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