📌 Research Question
This study tests whether the electoral rule itself affects ideological moderation among legislators by comparing Brazil's two federal chambers: senators, elected under a plurality-majority rule in state districts, and representatives, elected under a proportional rule. The cross-chamber comparison exploits the fact that the district unit is the state for both chambers but the electoral formulas differ.
📊 What Was Compared
- Senators (plurality-majority) versus deputies/representatives (proportional rule)
- Behavior measured at the level of roll-call votes across the two chambers
🔎 Data and Estimation
- Roll-call voting records from 1988 to 2010 were analyzed
- Legislators' ideal points were estimated using WNOMINATE to place actors on a common ideological scale
📈 Key Findings
- Evidence was found consistent with the hypothesis that plurality-majority incentives are associated with less moderate (more polarized) legislative behavior, while proportional rules are associated with comparatively more moderate behavior.
- The relationship is not universal: the effect appears in many cases but does not hold in every vote, period, or context examined.
⚖️ Why It Matters
- Results link electoral institutions to legislators' ideological positions in a real-world, within-country comparison, strengthening causal inference about how electoral formulas shape political behavior.
- Findings are relevant for debates over electoral reform and for scholars studying representation, party strategy, and legislative polarization.
