Improving CommonGround, an Online Peer Support Intervention for People Living With Long-Term Physical Health Conditions and Subthreshold Depression: Theory of Change-Informed Qualitative Study.

People living with long-term physical health conditions who are also experiencing subthreshold depression are at risk of developing major depression. In partnership with lived experience experts, clinicians, and software developers, we co-designed CommonGround, an online peer support and psychoeducation platform. CommonGround's Theory of Change (ToC) was also conceptualized to outline the intermediate outcomes (and associated indicators of whether such outcomes are achieved) needed to improve the mental health of the target population.

This qualitative study, informed by the ToC, aimed to examine the acceptability, usability, and intervention mechanisms of CommonGround and ultimately refine the ToC and corresponding intervention design ahead of definitive evaluation.

A nested qualitative study was conducted within a remote, 12-week feasibility randomized controlled trial comparing CommonGround (intervention group) to signposting to National Health Service (NHS) web pages (control group). Thirty-nine participants were purposively sampled and interviewed within 6 weeks postintervention about their experiences of CommonGround and trial participation. The interview schedule and thematic framework analysis were rooted in a pretrial ToC while being responsive to emergent themes.

Evaluating the assumptions and intermediate outcomes (via their indicators) refined our understanding of how CommonGround may support mental well-being. Overall, participants viewed CommonGround as an appropriate, safe space to access self-management information and support from others with a unique shared understanding of chronic illness. However, many participants felt more time was needed for genuine social relations to form and community culture to evolve. Anonymity helped foster a sense of safety but, for some participants, limited the formation of genuine connections. Other factors contributing to low engagement included personal circumstances (eg, limited time). Key suggestions for future development included creating a mobile app that would be easier and more intuitive to access and navigate.

CommonGround was considered an acceptable and appropriate space to access peer support, with the potential to positively impact psychological well-being by fostering shared understanding, support, and knowledge exchange. Beyond informing the future evaluation of CommonGround in a definitive trial, the refined ToC identifies the key preconditions, intermediate outcomes, and associated indicators, and assumptions that may underpin the acceptability and usability of digital peer support interventions in achieving their intended outcomes. We also demonstrate how evaluating and refining components of the ToC after the intervention had been implemented in the trial enabled a more nuanced understanding of how and why the intervention may work, for whom, under what circumstances, and informed changes to improve the co-designed intervention.