Measuring Partisan Bias in Single‐Member District Electoral Systems

McGhee, Eric

doi:10.1111/lsq.12033

Cited by 73 publications

(23 citation statements)

References 29 publications

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“…This election has a number of very competitive races that all have swung towards Party D. F Competitive even (Comp'). Similar to the previous election, but with no districts in the "counterfactual window" (i.e., between the majority party's statewide support and 50% -see (McGhee, 2014)). G Uncompetitive (Uncomp).…”

Section: Hypothetical Electionsmentioning

confidence: 95%

“…The only values of λ we know of that have been seriously considered in the literature are λ ∈ {0, 1, 2}, so we likewise restrict our attention to these. The efficiency gap (McGhee, 2014;McGhee & Stephanopoulos, 2015) is EG 1 . It has been suggested in several places (Whitford, 2016b;Cover, April 2018;Nagle, 2017) that wasted winning votes in a district should be relative to the losing party vote rather than to the 50% threshold.…”

Section: Gerrymandering Measuresmentioning

confidence: 99%

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A Comparison of Partisan-Gerrymandering Measures

Warrington

2019

Election Law Journal: Rules, Politics, and Policy

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We compare and contrast fourteen measures that have been proposed for the purpose of quantifying partisan gerrymandering. We consider measures that, rather than examining the shapes of districts, utilize only the partisan vote distribution among districts. The measures considered are two versions of partisan bias; the efficiency gap and several of its variants; the mean-median difference and the equal vote weight standard; the declination and one variant; and the lopsidedmeans test. Our primary means of evaluating these measures is a suite of hypothetical elections we classify from the start as fair or unfair. We conclude that the declination is the most successful measure in terms of avoiding false positives and false negatives on the elections considered. We include in an appendix the most extreme outliers for each measure among historical congressional and state legislative elections.

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Section: Hypothetical Electionsmentioning

confidence: 95%

Section: Gerrymandering Measuresmentioning

confidence: 99%

A Comparison of Partisan-Gerrymandering Measures

Warrington

2019

Election Law Journal: Rules, Politics, and Policy

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“…We now set geometry aside and discuss tools designed to measure a partisan gerrymander based on election outcomes. In [13], McGhee introduced a property he called the "efficiency principle," and Stephanopoulos and McGhee argued in [36] that this principle is necessary for any such tool. Stephanopoulos and McGhee have a nice description of the efficiency principle in [36]:…”

Section: The Efficiency Principlementioning

confidence: 99%

“…[The efficiency principle] states that a measure of partisan gerrymandering "must indicate a greater advantage for (against) a party when the seat share for that party increases (decreases) without any corresponding increase (decrease) in its vote share" [13]. The principle would be violated, for example, if a party received 55% of the vote and 55% of the seats in one election, and 55% of the vote and 60% of the seats in another election, but a metric did not shift in the party's favor.…”

Section: The Efficiency Principlementioning

confidence: 99%

Efficiency Gap, Voter Turnout, and the Efficiency Principle

Veomett

2018

Election Law Journal: Rules, Politics, and Policy

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Recently, scholars from law and political science have introduced metrics which use only election outcomes (and not district geometry) to assess the presence of partisan gerrymandering. The most high-profile example of such a tool is the efficiency gap. Some scholars have suggested that such tools should be sensitive enough to alert us when two election outcomes have the same percentage of votes going to political party A, but one of the two awards party A more seats. When a metric is able to distinguish election outcomes in this way, that metric is said to satisfy the efficiency principle.In this article, we show that the efficiency gap fails to satisfy the efficiency principle. We show precisely how the efficiency principle breaks down in the presence of unequal voter turnout. To do this, we first present a construction that, given any rationals 1/4 < V < 3/4 and 0 < S < 1, constructs an election outcome with vote share V , seat share S, and EG = 0. (For instance, one party can get 26% of the vote and anywhere from 1% to 99% of the seats while the efficiency gap remains zero.) Then, for any election with vote share 1/4 < V < 3/4, seat share S, and EG= 0, we express the ratio ρ of average turnout in districts party A lost to average turnout in districts party A won as a function in only V and S. It is well known that when all districts have equal turnout, EG can be expressed as a simple formula in V and S; we express the efficiency gap of any election as an equation only in V, S, and ρ. We also report on the values of ρ that can be observed in actual elections.arXiv:1801.05301v2 [physics.soc-ph]

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“…Justice Anthony Kennedy wrote that the Court had found "no discernible and manageable standard for adjudicating political gerrymandering claims," but his opinion left the door open for future gerrymandering cases by enumerating the properties that he believed a manageable standard would require. Motivated by Kennedy's criteria, Stephanopoulos and McGhee proposed their efficiency gap formula to measure the degree of partisan gerrymandering in an election [7], [11]. Their formula was one key to the plaintiffs' success in the Gill v. Whitford (2016) case, in which a Wisconsin court struck down the state assembly map.…”

Section: Introductionmentioning

confidence: 99%

Measuring Political Gerrymandering

Tapp

2019

The American Mathematical Monthly

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In 2016, a Wisconsin court struck down the state assembly map due to unconstitutional gerrymandering. If this ruling is upheld by the Supreme Court's pending 2018 decision, it will be the fist successful political gerrymandering case in the history of the United States. The efficiency gap formula made headlines for the key role it played in this case. Meanwhile, the mathematics is moving forward more quickly than the courts. Even while the country awaits the Supreme Court decision, alternative versions of the efficiency gap formula have been proposed, analyzed and compared. Since much of the relevant literature appears (or will appear) in law journals, we believe that the general math audience might find benefit in a concise self-contained overview of this application of mathematics that could have profound consequences for our democracy.

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Measuring Partisan Bias in Single‐Member District Electoral Systems

Cited by 73 publications

References 29 publications

A Comparison of Partisan-Gerrymandering Measures

A Comparison of Partisan-Gerrymandering Measures

Efficiency Gap, Voter Turnout, and the Efficiency Principle

Measuring Political Gerrymandering

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