Measuring the Integrity of Referendums – Introducing the Referendum Integrity Index

Referendums are used around the world to decide the most consequential questions countries face. Their democratic value depends on how each individual referendum is conducted. Yet we currently cannot measure this conduct systematically. Existing instruments capture the de jure potential of direct democracy at the country-year level or assess a small number of referendums in depth through expert surveys. This leaves referendum integrity incomparable across time, space and regime types. We approach this gap from the perspective of procedural legitimacy, defining integrity as referendum conduct in accordance with international standards and norms. To conceptualise referendum integrity, we draw on the Venice Commission's Revised Code of Good Practice on Referendums and the scientific literature. The resulting Referendum Integrity Index (RII) is codable through desk research from publicly available sources. It comprises three attributes, opinion formation, opinion realisation and legal framework. We validate the RII on the referendums in Türkiye 2017, Russia 2020 and Italy 2020 against the expert-based Direct Democracy Integrity Index (DDI). We find that it reproduces the ordering and evidential substance of the expert assessments without requiring expert panels. Because the RII travels to closed regimes and past cases, it lays the foundation for a worldwide, event-level dataset of referendum integrity.