Argentina provides unique insights into the impact of district magnitude on elections. Between 1985 and 2015, two natural experiments occurred when a lottery determined whether provinces elected their congressional representatives in odd or even numbers during midterms versus concurrently.

Data & Methods: Leveraged Argentina's mixed electoral system where half (descriptive representation) of the seats were filled every two years. This created situations where districts shifted from high to low magnitude across election cycles.

Key Findings:

• District magnitude significantly increases support for small political parties 📊

• It boosts the effective number of parties gaining parliamentary seats 🔥

• Elections become less proportional, reducing the gap between votes and seats ✅

Mechanism Insight: These effects stem from mechanical features of electoral rules rather than psychological voter behavior factors. This finding highlights a crucial distinction in understanding political representation systems.

This research demonstrates how seemingly small institutional changes can dramatically reshape election outcomes across multiple dimensions.