Joshua C. Yang, Carina I. Hausladen, Dominik Peters, Evangelos Pournaras, Regula Haenggli Fricker, Dirk Helbing

Digital Participatory Budgeting (PB) has become a key democratic tool for resource allocation in cities. Enabled by digital platforms, new voting input formats and aggregation have been utilised. Yet, challenges in achieving fairness and legitimacy persist. This study investigates the trade-offs in various voting and aggregation methods within digital PB. Through behavioural experiments, we identified favourable voting design combinations in terms of cognitive load, proportionality, and perceived legitimacy. The research reveals how design choices profoundly influence collective decision-making, citizen perceptions, and outcome fairness. Our findings offer actionable insights for human-computer interaction, mechanism design, and computational social choice, contributing to the development of fairer and more transparent digital PB systems and multi-winner collective decision-making process for citizens.