Why Measuring Electoral Competitiveness Depends on Votes Versus Seats

🧭 What's the problem?

Electoral competition is central across political science, yet there is no consensus on how to measure it at the district level across different electoral systems. Comparisons across single-member and multimember systems are especially sensitive to measurement choices.

🛠️ How the measurement debate is framed

Recent proposals offer general measures of competitiveness that combine two elements:

• explicit calculations of how votes translate into seats, and
• implicit assumptions about how political effort maps into votes (including how costly effort is).

This investigation examines how different assumptions about the effort-to-votes mapping change which units (votes or seats) are the appropriate basis for measuring competitiveness.

🔍 What was examined

• Types of electoral systems discussed: multimember proportional representation, single-member plurality, and runoff elections
• Alternative measurement units compared: vote-share-denominated measures versus vote-share-per-seat measures
• The role of the effort→votes mapping and effort costs in determining which unit best captures competitiveness

🔑 Key findings

• The assumed mapping from effort to votes directly affects the units in which competitiveness should be measured.
• Vote-share-denominated measures are favored; vote-share-per-seat measures are argued against.
• Whether multimember proportional representation appears more or less competitive than single-member plurality or runoff systems hinges on the chosen measurement units and the underlying effort-to-votes assumptions.

⚖️ Why it matters

Choices about measurement units are not neutral: they change empirical judgments about which electoral systems are more competitive. Careful attention to how effort converts into votes is therefore crucial for valid comparisons and for building theory about competition across electoral institutions.