Patient and public involvement and engagement in clinical trials at scale: Analysis of the first 3250 responses on the POrtal for Patient and Public Engagement in Dementia (POPPED).

INTRODUCTION: Patient and public involvement and engagement (PPIE) improves research quality but is often limited in scale. This study explored the potential for large-scale PPIE using a Web-based approach. METHODS: We created an online portal to gather public views on dementia research and a UK-based adaptive platform trial testing repurposed Alzheimer's disease drugs. Participants ranked four anonymized drugs and completed discrete choice experiments on treatment trade-offs. Analyses were stratified by sex, age, and dementia experience. RESULTS: Among 3250 people across 27 countries (87.4% UK-based), 79.6% expressed positive attitudes toward the trial. Metformin was the most preferred drug, followed by atomoxetine, isosorbide mononitrate, and levetiracetam. Probability of severe side effects was the most influential treatment attribute, followed by probability of mild side effects and type of evidence. Subgroup analyses supported the main findings. DISCUSSION: Web-based PPIE can effectively inform dementia research at scale and provides a reusable resource for other studies.