The so-called Efficiency Gap is often used to attack legislative maps, but relying on this statistical measure has major limitations according to WILL’s new report

The News: The Wisconsin Institute for Law & Liberty (WILL) just released its newest report, Behind the Lines: Investigating the Efficiency Gap in Redistricting. The report provides insight into the so-called Efficiency Gap, which left-leaning groups rely on to redraw legislative maps in courtrooms in Wisconsin and across America.

What is the Efficiency Gap? The efficiency gap tries to quantify how “efficiently” one party’s votes are spread over their winning districts. It often identifies high numbers of so called “wasted votes” in densely populated urban areas. If a map has a bad efficiency gap, oftentimes Left-leaning groups say that the map is gerrymandered when it reflects voter choices on where to live. Our report further explains this statistical measure and its limitations.

1. Arbitrary Cut Points. There is no clear legal standard to identify what makes a fair map or a gerrymandered map.
2. Wide Swings Based on a Few Districts. Gerrymandered maps can backfire on the party who drew them. When a map-drawer reaches for such a big electoral majority from such narrow victories that a “bad” year results in the opposition winning many races they weren’t “supposed” to win, that’s coined as “dummymandering.” Suddenly, an “unfair” gerrymander (as measured by the efficiency gap) becomes a normal one.
3. Uncontested Races. In many campaigns, incumbents run unopposed. The absence of any candidate skews the efficiency gap measure.
4. Majority-Minority Districts. The federal Voting Rights Act created stipulations to how maps can legally be drawn; for example, Wisconsin’s current map has five majority black Assembly districts and two majority Latino districts. These federal standards often contribute to the efficiency gap.
5. Political Geography. The data makes very clear that Democratic voters tend to be more concentrated in urban and (increasingly) suburban areas, while the largest Republican advantages are in rural areas. The realities of political geography are difficult to fully overcome.

• Behind the Lines: Investigating the Efficiency Gap in Redistricting, January 2024