Legislature size and council member diversity: evidence from Brazilian municipalities

Purpose This paper examines the impact of marginal changes in municipal council size on the diversity of candidates and elected councilors in Brazil, focusing on age, gender, race, and educational attainment. Understanding how institutional changes affect representation is crucial for assessing the effectiveness of legislative reforms in promoting political diversity. Design/methodology/approach We employ a regression discontinuity design (RDD) using population thresholds set by Constitutional Amendment 58/2009. The analysis covers the 2017–2020 and 2021–2024 electoral cycles, using data from the Brazilian Institute of Geography and Statistics (IBGE) and the Superior Electoral Tribunal (TSE). This methodology allows for a causal interpretation of the impact of small adjustments in council size on political representation. Findings Our results indicate that marginal increases in council size lead to a higher absolute number of non-white and high school-educated councilors but do not significantly change their proportional representation. Moreover, no significant effects are observed for gender or age diversity. These results suggest that the specific institutional adjustment examined—expanding council size within existing rules—does not meaningfully increase political diversity, highlighting the role of broader systemic factors. Originality/value This study contributes to the literature on political identity and institutional design by examining the interplay between legislative size and electoral outcomes. It also informs debates about whether structural changes in local governance effectively promote diversity or whether alternative interventions are needed.