Measuring Diversity in Representative Institutions

How diverse are representative institutions? Despite the theoretical and political relevance of this question, there is no standard measure of diversity in representative institutions, limiting systematic comparative research on diversity of representation. To address this, I introduce the Diversity of Representation Index (DORI), a multidimensional metric that quantifies institutional diversity by considering the variety and balance of represented groups, alongside the proportionality of their representation relative to their population shares—i.e., their descriptive representation. Using examples from national parliaments in Canada and Germany, and data on women and African Americans in all 50 U.S. state legislatures (2009–2021), I illustrate DORI's properties and applications, showing how assessing institutional diversity provides insights beyond single-group representation and relates to policy and democratic outcomes. DORI offers a valuable tool for representation studies, enabling robust empirical analysis of multidimensional political representation.