Abstract

Background
Waiting lists for clinical psychology services in the UK are long. A low-cost, transdiagnostic waiting list intervention could improve experiences and initiate processes of psychotherapeutic change. Guided Acceptance and Commitment Therapy (ACT) self-help holds promise in this regard – with evidence supporting its efficacy in other contexts – but has not yet been tested as a waiting list intervention. Moreover, research needs to explore underlying change-processes. Do outcomes (where present) follow the predictions of the Phase Model of Psychotherapeutic Outcome (PMPO), and are outcomes mediated by psychological flexibility, and its theorised sub-components, as posited by ACT?

Method
A multiple-baseline single-case experimental design was utilised to explore participant outcomes in psychological flexibility (and its theorised subcomponents), well-being, symptomatology, and life-functioning, during a 10-week phone-guided ACT self-help intervention. Analysis assessed levels of clinical/reliable change, and graphical plots of weekly scores were subjected to visual analysis utilising dual criterion and percentage of non-overlapping data methodology. Average percentage change on each measure was also calculated. Participants then engaged in a post-intervention change interview to triangulate results.

Results
Seven participants were recruited, with three participants completing the full 10-week intervention. Of the three who completed the intervention, two experienced clinically significant improvements in psychological flexibility, well-being, and symptomatology, and trends towards improvement in life-functioning, and the other participant experienced no significant changes in outcomes. The greatest average percentage improvement was in well-being, followed by symptomatology, then life-functioning – as predicted by the PMPO. However, visual analysis of weekly outcomes indicated a temporal order whereby symptomatology changed first. Links between psychological flexibility and outcomes were supported, with changes in psychological flexibility preceding or co-occurring with other outcomes, and indication that processes relating to “openness to experience” were most influential. Outcomes experienced by the four individuals who withdrew from the intervention were both supportive and counterintuitive to the main results; however, external life-factors, and the reduced number of completed weeks, reduce the generality of the results.
All participants attributed outcomes to both life-events and the intervention and placed emphasis on the positive impact of the guiding phone calls. Feedback also indicated that the intervention requires adaptation to improve accessibility prior to future implementation.

Discussion
Results indicate that a guided ACT self-help intervention produces outcomes that are (1) evidenced to predict later therapeutic results, (2) partially follow the temporal predictions of the PMPO, and (3) are likely mediated by changes in psychological flexibility (in particular “openness to experience”). The utility of the single-case experimental design has been supported, however, its limitations need to be considered when generalising results. Future research should continue exploration into ACT processes, and the application of guided ACT self-help interventions in such populations.