📌 What Changed

A Chilean electoral reform introduced proportional representation and larger district magnitudes while voting remained voluntary and legislative and presidential elections continued to be held concurrently. The reform lengthened legislative ballots by offering more candidate options.

🧾 How the Reform Was Studied

A difference-in-differences approach compares invalid votes in legislative versus presidential elections before and after the reform, exploiting the concurrent timing of the two races. Multiple DiD specifications were used and pre-trends were shown to be parallel.

🔎 Key Findings

• Invalid voting increased in legislative elections relative to presidential elections after the reform.
• The increase was larger in post-reform districts with higher district magnitude.
• This rise cannot be explained by pre-reform district characteristics.
• Heterogeneity analyses and a survey experiment point to the same mechanism: cognitive burden from a longer, more complex ballot.

💡 Why It Matters

The results reveal an understudied consequence of high-magnitude proportional systems: offering more options can reduce the likelihood that some voters cast a valid vote. Even voters motivated enough to participate in the top-ticket (presidential) race may be demobilized—in terms of valid voting—on longer legislative ballots, especially those vulnerable to cognitive burden.