| 摘要 | Key Points
The “efficiency gap,” which seeks to measure “wasted votes” for the parties, is a clever addition to the burgeoning body of literature that attempts to quantify partisan gerrymandering.
The efficiency gap metric is nevertheless a poor metric for courts to use to resolve litigation, in part because many things besides partisan gerrymandering can influence the size of an efficiency gap.
In addition, the efficiency gap fails to give an objective answer to the fundamental question of gerrymandering litigation: How much gerrymandering is too much?
However, courts ought not abandon completely attempts to police partisan gerrymandering. Use of a rational review standard could help prevent the most egregious gerrymanders from surviving.
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Executive Summary
For over 30 years, the Supreme Court has held that partisan gerrymandering can theoretically violate the US Constitution. However, the Court has never struck down a plan as a partisan gerrymander. This is because the Court has been unable to agree on a judicially manageable standard to determine how much gerrymandering is too much.
In recent years, political scientists and mathematicians have offered various metrics to measure partisan gerrymandering. One of these tests, the efficiency gap, made headlines when federal courts in Wisconsin and North Carolina used the statistic to justify striking down maps. As of this writing, the North Carolina case is pending before the Supreme Court.
The efficiency gap is an interesting metric that likely tells us something about gerrymandering. It is a flawed metric, however, for several reasons. For example, the efficiency gap can be changed if a party runs an unusually strong candidate or has an incumbent unexpectedly die or retire. This creates a substantial problem: It is difficult, and at times impossible, to sort out how much of an efficiency gap is due to these factors and how much of it is due to gerrymandering. Likewise, the efficiency gap does not account directly for partisan clustering, which can also influence its score. It is also pseudo-normative, smuggling in several assumptions about what a gerrymander actually is; by adopting it, a court may be deciding things it does not even realize it is deciding. Finally, the efficiency gap does not truly answer the question of how much gerrymandering is too much. It merely pushes the question back a step, arbitrarily selecting a cutoff and then placing a statistical gloss on it.
Nevertheless, the Court should not abandon policing partisan gerrymandering altogether. Justice Anthony Kennedy once warned about a state simply declaring that all the state’s seats should go to Republicans or Democrats. A similar result could be obtained and would be equally damaging to democracy if a state were to completely abandon all traditional redistricting criteria to push through a map that would tend to elect only its partisans. To help police the outer limits of gerrymandering, the Court should consider proceeding on a rational review standard.
Introduction
The Supreme Court of the United States has struggled to define the limits of partisan gerrymandering for over 30 years. For over a decade, the Court had been largely silent on the matter. Then, in 2016, a federal court in Wisconsin struck down a map as a partisan gerrymander for the first time in decades. In that case, Gill v. Whitford, plaintiffs urged the Court to adopt a test based largely on a statistic known as the “efficiency gap,” which defines a gerrymander in terms of “wasted votes.”1 Although the Court did not accept the plaintiffs’ invitation to apply the efficiency gap directly, a federal court in North Carolina and a state court in Pennsylvania have since spoken favorably of the efficiency gap, albeit to different degrees.
In June 2018, the Supreme Court reversed the Wisconsin court decision on a procedural issue known as “standing.” It sent the case back to the district court, where plaintiffs amended their complaint to add additional plaintiffs that comply with the standing requirement. The North Carolina case is currently pending before the Supreme Court, while the remand of the Whitford decision is currently stayed, pending the Supreme Court’s decision. Cases pending in federal courts in Michigan and Ohio raise efficiency gap– related issues as well. Obviously, if the Supreme Court accepts the North Carolina challenge, efficiency gap claims will multiply. But even if it turns away the challenge, plaintiffs will likely try their hands in state courts, where they have found a receptive audience on at least one occasion (in Pennsylvania).
Since we will likely be dealing with claims arising from the efficiency gap for quite some time, this report provides an overview of the major arguments for and against it. It explains the motivation behind the efficiency gap, the statistic itself, and the potential problems with the gap. The report concludes that while the efficiency gap is a conceptually useful tool for an academic understanding of gerrymandering, it is deeply problematic when used as part of a legal test. While this report will not give an exhaustive account of every nuance of the efficiency gap—the expert testimony in these cases stretches over hundreds of pages—a careful reader should emerge with a solid understanding of the legal test, how the statistic is calculated, and its drawbacks.2
Read the full report.
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