Acceptance and Commitment Therapy for adolescents: A systematic review of online self-help interventions, and An empirical study validating a measure of psychological flexibility

With increasing rates of mental health difficulties in young people placing demand on specialist mental health services, alternative forms of support are needed to prevent difficulties arising and intervene early when they do, to reduce escalation. One such approach involves providing universal interventions, including online self-help. In recent years, the interest in Acceptance and Commitment Therapy (ACT) as an intervention for mental health and well-being in young people has grown. ACT aims to improve psychological flexibility, the ability to adapt and respond effectively to situations and internal experiences, while remaining open to the present moment and acting in alignment with one's values. However, a challenge in ACT research is that conclusions regarding effectiveness are limited by insufficient measurements of psychological flexibility in young people. The aim of this research is to review the literature to evaluate the effectiveness of universal, digitally delivered self-help ACT interventions for young people on mental health, well-being and psychological flexibility outcomes, and to validate a comprehensive measure of psychological flexibility processes in young people. The first paper in this thesis systematically reviewed the literature relating to of universal, digitally delivered self-help ACT interventions for young people. Universal interventions can be delivered to a whole population and aim to foster positive mental health and well-being, and self-help is one format in which they can be delivered. Self-help involves individuals following a treatment process individually and have increasingly been delivered digitally to extend access to support. Previous research and reviews have examined universal and online self-help interventions, and found them to be a promising source of support for young people. However, none have exclusively focused on these interventions using ACT. Studies were eligible if the ACT intervention targeted at least two processes of psychological flexibility, delivered to young people between 10 and 25 years old, and had outcome measures relating to mental health, well-being and psychological flexibility. Searches of relevant databases provided 11 studies which met inclusion criteria. Subsequently, the studies were quality assessed and findings were synthesised using a narrative approach. The results between studies varied. A majority reported significant improvements in mental health and well-being outcomes. However, less than half of the studies found improvements in ACT process measures. The review was unable to draw firm conclusions regarding the effectiveness of universal, digitally delivered self-help ACT interventions due to heterogeneity in study design, intervention content and outcome measures used. The second paper in this thesis is an empirical paper which aimed to validate the Comprehensive assessment of Acceptance and Commitment Therapy processes for youth (CompACT-Y). ACT interventions have been shown to be effective for a range of difficulties in children and young people, however there are existing challenges in measuring psychological flexibility in this population. The CompACT-Y was administered alongside other measures of psychological flexibility subprocess, mental health, well-being and behaviour to determine its factor structure, validity and internal reliability. A total of 334 young people from six schools across the UK participated in the research. The study resulted in a 19-item version of the CompACT-Y with a three factor structure, which aligned with ACT and psychological flexibility theory. The CompACT-Y also correlated as expected with other measures of psychological flexibility for young people, suggesting good convergent validity. It also correlated with mental health, well-being and behavioural measures in line with theoretical understanding of psychological flexibility, indicating good concurrent validity. A validated, comprehensive measure of psychological flexibility has implications for future research on ACT for children and young people, and addresses some of the issues of measuring psychological flexibility both in research and clinical practice. This research contributes to the understanding of ACT and psychological flexibility in children and young people by highlighting methodological issues of studies included in the systematic review, and addresses some of these issues by offering a valid measure of psychological flexibility, particularly for values and committed action subprocesses, as other validated measures for these constructs do not exist. This research also adds to evidence about the role of psychological flexibility in mental health and well-being in children and young people