A Comprehensive Standard for Partisan Gerrymandering

The ‘efficiency gap’ standard now before the Supreme Court in Gill v. Whitford would only be part of an overall standard for partisan gerrymandering. This article outlines a comprehensive standard for partisan gerrymandering that incorporates the efficiency gap, a standard for intent, and the notion of baseline congressional districts.

A comprehensive standard for partisan gerrymandering requires three components:

  • A standard for determining discriminatory effect
  • A standard for discriminatory intent, and
  • A standard for process-neutral congressional districts

Each of these is described individually below, and then they are woven together into a comprehensive standard for partisan gerrymandering.

A Standard for Discriminatory Effect: Percentage-based Efficiency Gap with a Low Threshold

As I outlined in depth in a previous post “Will the Supreme Court Only Close the Door on Partisan Gerrymandering Halfway?” [http://bit.ly/2xKuHOQ], even if the Supreme Court affirms the justiciability of partisan gerrymandering in general by affirming Whitford and the use of the ‘efficiency gap’ specifically to measure partisan asymmetry, the Court needs to a) express the standard in percentage terms for congressional elections, not seats, and b) establish a low tolerance of no more than 5–10% inefficiency.

This would be the first building block of an overall standard.

A Standard for Discriminatory Intent: Excessive Discriminatory Effect Shows Intent

As I outlined in the same previous post, the Court could also rule that excessive discriminatory effect prima facie demonstrates discriminatory intent. The logic is simple.

If you believe:

  • Every state has a set of congressional districts that are sufficiently politically symmetric; and
  • States can reasonably consider some of those plans when redistricting; and
  • States can evaluate the degree of partisan symmetry/asymmetry of different plans.

Then you must believe that excessive partisan asymmetry in resulting plans also demonstrates intentional discrimination for partisan advantage.

Hence, the Court could rule that while the efficiency gap measures discriminatory effect, but it also shows discriminatory intent. In other words, they could collapse the standard for discriminatory intent into the standard for discriminatory effect.

A Standard for Process-Neutral Congressional Districts: Baseline Congressional Districts

A comprehensive standard for partisan gerrymandering needs one more concept: baseline congressional districts.

While there are relatively well established traditional districting principles,[1],[2],[3] there has been little agreement on how to apply them in the process of redistricting. Within the constraints that districts must be contiguous and have roughly equal populations using decennial census data, there has been little agreement about the relative priorities of the other criteria including political fairness. As a result, it can seem nigh impossible to evaluate whether any particular set of congressional districts represents a reasonable, lawful balance of these principles.

The concept of ‘baseline congressional districts’ dramatically simplifies the problem space and provides an easy-to-understand benchmark against which judges can evaluate the districts in question. Baseline districts are described in depth in another previous post “Baseline Congressional Districts: A Benchmark for Comparison” [http://bit.ly/2zlQNrL] which provides examples for two of the most gerrymandered states, North Carolina and Maryland.

In a nutshell though, every state has a well-defined baseline set of congressional districts that maximize the compactness and cohesion[4] of the districts while keeping district populations roughly equal. These baseline districts are composed almost entirely of whole counties, except when counties are too big to be in a single congressional district or in a few cases where counties need to be split to keep district sizes roughly equal.

Baseline districts optimize neutral traditional districting principles without considering politics. Hence, they are, by definition, free of explicit intent to gerrymander for partisan advantage. Due to the vagaries of political geography — where different kinds of people live in a state — baseline districts are not necessarily fair politically though. There may be naturally occurring discriminatory effect due to liberal/conservative urban/rural polarization[5] or the distribution of minorities throughout a state, race and ethnicity being a close proxy for aggregate voting tendencies.

Tying It All Together

With these three concepts in hand, we can now describe a comprehensive standard for partisan gerrymandering.

In loose, informal terms, it is simply:

  • The congressional districts for states should be at least as politically fair as the baseline districts, unless those are excessively unfair politically.
  • In those cases, states should “denormalize” the baseline districts enough to make them sufficiently fair politically.
  • States may, however, choose to make their congressional districts even more fair politically than these standards, but in no case may states use congressional districts that are less fair politically.
  • If the districts in question violate a) or b), no separate determination of discriminatory intent is required, as the discriminatory effect is a priori intentional.

where “politically fairness” refers to the efficiency gap and the threshold for how much is allowed.

A more formal, detailed procedure is shown visually in Exhibit 1 and described below:

1. Who controlled the redistricting process?

As a matter of evidence, it does not matter. In all cases, proceed to Step 2.

When a single party controls the redistricting process, the results are suspect, of course. But as the Brennan Center report Extreme Maps[6] shows though, congressional district maps can be quite biased even when drawn by independent commissions or even modified by courts. Moreover, a biased map is just as unfair to voters, regardless of who drew it.

2. Do the baseline districts (BD) have less partisan asymmetry (more partisan symmetry) than the efficiency gap threshold (EGT)?

If “Yes,” go to Step 3. If “No,” go to Step 4.

3. When BD < EGT, there are two cases to consider:

a. If the districts in question (CD1 or CD2) have more partisan asymmetry than BD, then the districts are too asymmetric. No separate determination of discriminatory intent is required, because excessive discriminatory effect demonstrates discriminatory intent.

In this case, there is no tension between partisan symmetry and neutral districting principles. The baseline districts are better on all dimensions — more compact, more cohesive, and more symmetric — and should be adopted.

b. The only acceptable reason for a state to deviate from the baseline districts should be to make them even more fair politically, have more partisan symmetry (CD3).

4. When BD ≥ EGT, there are again two cases to consider:

a. If the districts in question (CD1 or CD2) have more partisan asymmetry than EGT, the districts are again too asymmetric. Again, no separate determination of discriminatory intent is required.

The districts should be redrawn so that their efficiency gap is less than EGT. The resulting districts will, by definition, be less compact and cohesive than BD, but they will achieve an acceptable degree of partisan symmetry.

b. Of course, a state could again choose to draw districts (CD3) that are even more fair politically, have more partisan symmetry, but less compact and less cohesive.


A complete standard for partisan gerrymandering would incorporate the ‘efficiency gap’ now before the Supreme Court, expressed in percentage terms and with a low threshold to gauge discriminatory effect, a standard for discriminatory intent collapsed into that standard, and a standard for process-neutral congressional districts, baseline congressional districts.

This is the third in a series of articles on redistricting and partisan gerrymandering.

Exhibit 1 — A Standard for Partisan Gerrymandering

[1] “Voting Rights and Democracy: The Law and Politics of Districting,” Richard K. Scher et al.

[2] “The Traditional and the less Conventional, but never dull, Cast of Redistricting Principles,” Karin Mac Donald, retrieved from http://redistrictinginstitute.org/wp-content/uploads/2011/01/Traditional-Redistricting-Principles-Karin-Mac-Donald.pdf.

[3] “The Realist’s Guide to Redistricting: Avoiding the Legal Pitfalls,” J. Gerald Hebert.

[4] “Cohesion” is shorthand for the traditional districting principle of respect for political boundaries & topographical features, e.g., regions, counties, cities, towns.

[5] https://thinkprogress.org/supreme-court-snatches-victory-away-from-the-forces-of-gerrymandering-8a92d35b87db#.fmb1fmt5i

[6] Extreme Maps, the Brennan Center for Justice [http://bit.ly/2r6654e].

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