[EL] Gerrymandering, the wasted votes / efficiency method, and geographic concentration

[Eric McGhee]

I invented the efficiency gap, yet I would still agree with Michael that it seems unlikely a ruling for the plaintiffs in Whitford would rely exclusively on that metric.  (I would take issue with Michael’s claim that the efficiency gap is a “simple transformation” of existing measures under all conditions, but that’s another story.)  It’s also worth noting that the legal standard Nick Stephanopoulos and I proposed (see http://chicagounbound.uchicago.edu/uclrev/vol82/iss2/4/) would still treat a plan’s observed efficiency gap as only one step in a process that would also allow a state to defend its plan as unavoidable for other reasons.

Fortunately for the Whitford plaintiffs, every conceivable measure of bias or intent suggests the WI plan is a strong outlier.  This includes a variety of tests that account for the state’s underlying political geography.  To my mind, this makes the Whitford case less a test of a particular standard or measure, and more a test of whether the court really wants to get involved in partisan gerrymandering in the first place.

Eric McGhee

From: law-election-bounces at department-lists.uci.edu [mailto:law-election-bounces at department-lists.uci.edu] On Behalf Of Michael McDonald
Sent: Wednesday, June 14, 2017 4:12 PM
To: Election Law Listserv <law-election at uci.edu>
Subject: Re: [EL] Gerrymandering, the wasted votes / efficiency method, and geographic concentration

The efficiency gap is a simple transformation of prior seats to votes partisan bias (gerrymandering detection) measures. If one party wins more than 50% of the seats with 50% of the vote, all measures will indicate that the party is favored in a redistricting plan. For this reason, the efficiency gap is no more or less challenged than other partisan bias measures and I suspect Justice Kennedy will find it wanting for a bright line that identifies when a constitutional violation has occurred, as he has done with every other measure presented before him.

Simulations are problematic for another reason. Redistricting is such a complex graph partitioning problem that enumeration of all feasible redistricting plans is impossible in finite time. As a consequence, we cannot know the properties of any simulation algorithm that does not generate all feasible plans with equal probability. The only algorithm that is guaranteed to create plans with equal probability is one that randomly assigns blocks to districts and rejects resultant plans than are not legal. (This is similar to random sampling from a survey perspective.) Unfortunately, this algorithm produces feasible plans with exceedingly low frequency as to make it impossible to use in finite time. All other proposed simulation algorithms have never been proven that they can randomly sample. Indeed, we have shown that two proposed algorithms fail random sampling on a small toy example (see: https://papers.ssrn.com/sol3/papers.cfm?abstract_id=2583528<https://papers.ssrn.com/sol3/papers.cfm?abstract_id=2583528>). Failure to demonstrate the ability to randomly sample means that an algorithm could be biased in unknown ways, and might indicate the presence of a gerrymander when none exists, or fail to detect a gerrymander when one exists.

The paper I link to describes the method of revealed preferences that the Florida and Wisconsin courts applied to determine a partisan gerrymander occurred. The method of revealed preferences simply looks at the adopted plans as they were developed and traces how partisan goals were elevated over traditional redistricting principles. In both cases, the courts waved legislative privilege to enable plaintiffs to see how the legislature incrementally traded off state constitutional or other traditional redistricting principles for partisan advantage through the course of generating test maps. In Florida, the efficiency gap was not put before the court in evidence, and simulations failed so spectacularly that the district court judge did not even bother to describe the evidence in his ruling. In Wisconsin, the court found a traditional partisan bias measure created by a consultant to the legislature was informative, as was the efficiency gap, in tracing out the legislature's preferences. I suspect that if Kennedy rules favorably for the Wisconsin plaintiffs, it will be on on the strength of the revealed preferences illuminated by applying both partisan bias measures to the test plans defendants produced in discovery, and not on the efficiency gap alone.

============
Dr. Michael P. McDonald
Associate Professor, University of Florida
352-273-2371
www.electproject.org<http://www.electproject.org>
@ElectProject

On Wed, Jun 14, 2017 at 4:52 PM, Mark Scarberry <mark.scarberry at pepperdine.edu<mailto:mark.scarberry at pepperdine.edu>> wrote:
My thanks to Bruce and to another list member who replied off-list. Has this point been made in any of the briefs?

Mark

Mark S. Scarberry
Pepperdine University School of Law
________________________________
From: Bruce E Cain <bcain at stanford.edu<mailto:bcain at stanford.edu>>
Sent: Wednesday, June 14, 2017 1:43:49 PM
To: Mark Scarberry; Election Law Listserv
Subject: Re: [EL] Gerrymandering, the wasted votes / efficiency method, and geographic concentration

Mark

The efficiency gap is highly problematic for many reasons, and would be especially bogus for the reason you suggest if cross-sectional, over time data are used  rather than simulations, as is the case in Whitford…see Wendy Tam Cho’s web page or email her at <wendycho at illinois.edu<mailto:wendycho at illinois.edu>> for several forthcoming publications on this topic…

B

From: Mark Scarberry <mark.scarberry at pepperdine.edu<mailto:mark.scarberry at pepperdine.edu>>
Date: Wednesday, June 14, 2017 at 1:30 PM
To: Election Law Listserv <law-election at uci.edu<mailto:law-election at uci.edu>>
Subject: [EL] Gerrymandering, the wasted votes / efficiency method, and geographic concentration

I'm sure someone must have made the following point (if it is right).

The wasted votes / efficiency method for measuring partisan gerrymandering would seem to take "one person one vote" to the next level. It would benefit parties (currently the Democratic party) whose supporters are geographically concentrated.

Is that observation correct? Cites would be appreciated.

Mark

Mark S. Scarberry
Pepperdine University School of Law

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