Fact check: How does the efficiency gap measure compare to other gerrymandering metrics?

1. Summary of the results

The efficiency gap is a quantitative measure developed by Nicholas Stephanopoulos and Eric McGhee that measures partisan gerrymandering by calculating the difference in "wasted votes" between parties ^[1]. This metric has gained significant attention as a tool for identifying unconstitutional partisan gerrymandering, with proposed thresholds above which district plans would be presumptively unconstitutional ^[2].

When compared to other gerrymandering metrics, the efficiency gap stands alongside several alternative measures:

• Mean-median difference - another test used to evaluate partisan gerrymandering ^[1]
• Partisan bias - a measure that the efficiency gap is argued to be superior to because it doesn't require estimation of hypothetical election results ^[3]
• Declination - mentioned as another metric for measuring partisan gerrymandering ^[4]

The Brennan Center has utilized a simplified version of the efficiency gap to analyze congressional map fairness ^[5]. In practical application, analysis shows that the proposed Freedom to Vote Act's presumption of extreme partisan bias would have been triggered in 19 states using efficiency gap standards, with hundreds or thousands of alternative maps available that wouldn't be categorized as partisan gerrymanders ^[5].

2. Missing context/alternative viewpoints

The original question lacks several important contextual elements that emerge from the analyses:

• Geographic limitations: The analyses reveal that geography can sometimes prevent the creation of perfectly fair maps, and parties tend to get higher seat shares than vote shares in deep-red or deep-blue states ^[6]. This suggests that efficiency gap measurements must account for natural geographic clustering of voters.
• Practical implementation challenges: While statisticians and political scientists have developed various ways to quantify partisan advantage attributable to gerrymandering ^[7], the analyses don't provide comprehensive comparisons of how these different metrics perform in real-world scenarios.
• Legal and constitutional framework: The efficiency gap has been proposed as a constitutional standard with specific thresholds ^[2], but the analyses don't fully explore how other metrics fare in legal contexts or their acceptance by courts.
• Bipartisan commission outcomes: Analysis of California's congressional map, drawn by a bipartisan commission, demonstrates that even non-partisan processes can result in maps that might appear gerrymandered under certain metrics ^[6].

3. Potential misinformation/bias in the original statement

The original question itself doesn't contain misinformation, as it's posed as an inquiry rather than making claims. However, there are potential areas where incomplete understanding could lead to bias:

• The question assumes that comparative analysis between metrics is readily available and conclusive, when the analyses show that direct comparisons between the efficiency gap and other metrics are limited in the available sources ^{[7] [4]}.
• The framing doesn't acknowledge that different metrics may serve different purposes or have varying strengths and weaknesses in different contexts.
• There's an implicit assumption that gerrymandering metrics can be objectively compared without considering the political and legal contexts in which they operate, when the analyses suggest that practical application involves complex considerations beyond pure mathematical comparison ^{[5] [6]}.