Vinayak Anand Kumar

• Chronic and non-communicable diseases present ongoing challenges for healthcare systems worldwide. Digital Health Interventions (DHIs) provide a promising solution by empowering patients to engage in health-related decisions and manage their behaviours. At present, many DHIs suffer from low user adoption or fail to progress beyond research. This thesis analyses the design, build, and evaluation of such tools to guide the effective co-creation of DHIs. Across five studies, this thesis examines the design, build, and evaluation of DHIs. The first two studies explore how to effectively plan the co-creation of DHIs, identifying both facilitators and challenges. The second study applies co-creation methods to incorporate end users in developing design specifications for a DHI. The third study evaluates the impact of including end users in the build phase, whilst the final two studies assess evaluation strategies, demonstrating how synthetic data and machine learning can be used to manage missing data and predict intervention outcomes. Findings highlight the importance of adaptive, inclusive design processes, careful planning of co-creator involvement, and the application of behavioural science across all phases. The thesis offers practical guidance for future researchers, emphasising the value of empowering patients, addressing attrition, and applying predictive analytics to maximise the real-world impact of DHIs.