🔎 How a National Reform Became a Natural Laboratory

This study leverages an early twentieth-century Argentine electoral reform that was applied unevenly across districts, producing a rare setting where some districts oscillated between electoral systems across elections. That asymmetric implementation creates a natural experiment for assessing whether more proportional rules affect voter turnout.

📐 Design That Compares Districts Over Time

• Uses the reform’s staggered, district-level implementation to construct a difference-in-differences (DiD) research design.
• Compares turnout in districts that switched between multi-member plurality and a slightly more proportional system to districts that did not, taking advantage of multiple election waves.

📊 What the Shift Changed, Quantitatively

• The reform moved rules from multi-member plurality toward greater proportionality by removing roughly one-third of contested seats from the dominant party’s guaranteed control.
• That change is associated with an average increase in turnout of four percentage points.

⚙️ How Proportionality Affected Party Behavior and Competition

• More proportional rules increased the probability that smaller parties won seats.
• This improved seat access encouraged strategic party entry and intensified electoral competition both between parties and within parties (intra-party competition for seats).

💡 Why These Results Matter

• Complements prior quasi-experimental findings that focus on European democracies by providing evidence from Latin America.
• Demonstrates that parties can and do adapt immediately to rule changes, altering entry and competition incentives.
• Challenges the claim that proportionality does not influence turnout in Latin American contexts.

The evidence supports a causal link from modest increases in proportionality to higher participation via changes in party entry and competitive dynamics.