Faulty Votes: The Hidden Cost of PR Election Complexity

We seek to assess how informational challenges in open-list proportional representation (OLPR) systems contribute to higher incidence of “faulty” votes compared to majoritarian systems. We define three types of faulty votes: spoilt votes and votes attributable to ballot primacy or list primacy effects. Using data from simultaneously held Polish OLPR and SMD local elections, we find significantly higher rates of faulty votes in OLPR systems than in SMD systems—an estimated 12.87% more eligible voters cast a faulty vote under OLPR. The difference is even more stark when calculated as a percentage of actual voters, with over 25% more faulty votes under OLPR. Our findings suggest that the increased complexity of OLPR systems leads to lower-quality votes. This “PR blow” is similar in magnitude but opposite in direction to the well-documented “PR boost” in turnout. We offer policy recommendations to mitigate faulty votes in OLPR systems, including simplifying ballots, using smaller districts, and randomizing candidate order.