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Abstract

Background
Long-term (previously termed chronic) depression is associated with significant personal, social and economic consequences often resulting in a poor quality of life for individuals. Effective treatments that improve quality of life for individuals with chronic depression remain limited. DIALOG+, a solution-focused and person-centred intervention, guided by a tablet-based application, was developed to address these challenges. Initially proven to be effective in handling psychotic disorders, this study adapted and evaluated DIALOG+ for individuals with chronic depression.

Objectives
The research aimed to adapt and assess the feasibility, clinical and cost-effectiveness of DIALOG+ for improving quality of life, reducing depression severity and enhancing treatment satisfaction among individuals with chronic depression.

Setting
The study was conducted across nine National Health Service sites in England, encompassing both urban and rural settings. Participants were recruited from outpatient Community Mental Health Teams, including primary care services, such as increasing access to psychological therapies, ensuring diverse sociodemographic characteristics and clinical contexts. Clinicians from varied professional backgrounds, including mental health nurses, psychiatrists and social workers, were trained to deliver the intervention.

Design
The study comprised multiple interlinked work packages:

Systematic review: existing recruitment and retention strategies for trials with individuals with depression.
Focus groups and pilot study: to adapt the intervention.
Small-scale cluster randomised controlled trial: testing feasibility of the intervention and trial processes.
Large multisite pragmatic cluster randomised controlled trial: including a nested qualitative process evaluation and economic evaluation.
Training and implementation study: evaluating feasibility and applicability within different clinical services.

A total of 366 participants with chronic depression were included. Patients were clustered by clinician and clusters randomised 1 : 1 to receive DIALOG+ or an active control (treatment as usual with DIALOG scale completion). Participants were assessed at baseline, 3, 6 and 12 months. The primary outcome was subjective quality of life, measured by the Manchester Short Assessment of Quality of Life at 12 months. Secondary outcomes included depression severity (Montgomery–Åsberg Depression Rating Scale, Beck Depression Inventory-II), treatment satisfaction (Client Satisfaction Questionnaire-8) and health-related quality of life (EuroQol-5 Dimensions, five-level version). Economic evaluation was conducted from National Health Service and Personal Social Services perspectives. Process evaluation involved implementation data and interviews with participants and clinicians to assess intervention experience.

Results
The systematic review highlighted the overall poor quality of reporting for existing trials of psychosocial intervention, with many trials failing to outline information on recruitment and retention. It was demonstrated that the intervention was feasible and acceptable to individuals with chronic depression during the feasibility and pilot work. Although the intervention remained unchanged, feedback from the initial phases of the project, alongside lived experience input led to changes in intervention training, which included the addition of case vignettes specific to long-term depression. Within the cluster randomised controlled trial, at 12 months, the DIALOG+ group exhibited a borderline significant improvement in Manchester Short Assessment of Quality of Life scores compared to the control group (adjusted mean difference: 0.18, p = 0.05). This equated to an average improvement of 1 point on 2 of the 12 Manchester Short Assessment of Quality of Life domains. There were no significant differences in any other outcome at 6 and 12 months. However, longitudinal analysis demonstrated significant reductions in Montgomery–Åsberg Depression Rating Scale and Beck Depression Inventory-II scores in the DIALOG+ group at 12 months (p < 0.01), and participants reported better coping strategies and resilience in managing depressive symptoms. The intervention was associated with an incremental cost-effectiveness ratio of £4749 per quality-adjusted life-year gained. Probabilities of cost-effectiveness were 79.8% at a willingness-to-pay threshold of £20,000/quality-adjusted life-year and 87% at £30,000/quality-adjusted life-year.

Despite high retention rates (73% at 12 months), challenges included attrition due to COVID-19 disruptions, with whole clusters lost during early lockdown phases. Fidelity to the intervention protocol varied, with just under a third of participants receiving fewer than three sessions (the minimum recommended dose). Nonetheless, the observed treatment effects were robust across varying levels of engagement.

Findings from the process evaluation were increased satisfaction with care, improved therapeutic relationships and a greater sense of empowerment. However, some participants noted challenges with the structured nature of the intervention and the use of technology. This was mirrored by the clinician experience, which found DIALOG+ easy to integrate into routine care and appreciated its structured, patient-centred approach. Barriers included variability in implementation fidelity and technological challenges, particularly during remote delivery.

Limitations
Key challenges across the programme included: (1) disruption from the COVID-19 pandemic, leading to adaptations in delivery methods and pauses in recruitment; (2) implementation variability, with some clinicians requiring additional training to maintain fidelity within the cluster randomised controlled trial; and (3) attrition and missing data, particularly in measures for economic evaluation, which necessitated the use of multiple imputation for some analyses.

Conclusions
The DIALOG+ demonstrated small but clinically meaningful improvements in quality of life and reductions in depression severity for individuals with chronic depression. While the improvement in Manchester Short Assessment of Quality of Life scores was very modest, it represents a potential gain for a population with long-term difficulties and low baseline quality of life. The probabilities of the intervention being cost-effective in comparison to active control at the National Institute for Health and Care Excellence recommended willingness-to-pay thresholds were high. The intervention was also associated with high patient and clinician satisfaction. These findings support the wider implementation of DIALOG+ in routine mental health care, with adaptations for remote delivery and ongoing support for clinicians.

Future directions
Further research is needed to explore the long-term impacts of DIALOG+ on quality of life and depression severity. Peer-delivered models and strategies to enhance engagement with the intervention may strengthen its effectiveness and scalability.

Publication Type:	Article
Additional Information:	Copyright © 2026 Bird et al. This work was produced by Bird et al. under the terms of a commissioning contract issued by the Secretary of State for Health and Social Care. This is an Open Access publication distributed under the terms of the Creative Commons Attribution CC BY 4.0 licence, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. See: https://creativecommons.org/licenses/by/4.0/.For attribution the title, original author(s), the publication source – NIHR Journals Library, and the DOI of the publication must be cited.
Subjects:	B Philosophy. Psychology. Religion > BF Psychology R Medicine > RC Internal medicine > RC0321 Neuroscience. Biological psychiatry. Neuropsychiatry
Departments:	School of Health & Medical Sciences School of Health & Medical Sciences > Department of Population Health & Policy
SWORD Depositor:	Symplectic Administrator

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