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

[Michael McDonald]

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). 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
@ElectProject

On Wed, Jun 14, 2017 at 4:52 PM, Mark Scarberry <
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>
> *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> for
> several forthcoming publications on this topic…
>
> B
>
> From: Mark Scarberry <mark.scarberry at pepperdine.edu>
> Date: Wednesday, June 14, 2017 at 1:30 PM
> To: Election Law Listserv <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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