No. 16-1161
IN THE

Supreme Court of the United States
________________

BEVERLY R. GILL, ET AL.,
Appellants,
v.
WILLIAM WHITFORD, ET AL.,
Appellees.
________________
ON APPEAL FROM THE UNITED STATES DISTRICT COURT
FOR THE WESTERN DISTRICT OF WISCONSIN
________________
BRIEF OF BERNARD GROFMAN AND
RONALD KEITH GADDIE AS AMICI CURIAE
IN SUPPORT OF NEITHER PARTY
________________
Thomas M. Bondy
Avi Daniel Rosenblit
ORRICK, HERRINGTON &
SUTCLIFFE LLP
1152 15th Street NW
Washington, DC 20005

E. Joshua Rosenkranz
Counsel of Record
Rachel Wainer Apter
Hannah Garden-Monheit
ORRICK, HERRINGTON &
SUTCLIFFE LLP
51 West 52nd Street
New York, NY 10019
(212) 506-5000
jrosenkranz@orrick.com
Counsel for Amici Curiae

 i
TABLE OF CONTENTS
Page
Table of Authorities ................................................. iii
INTERESTS OF AMICI CURIAE ............................ 1
INTRODUCTION AND SUMMARY OF
ARGUMENT ................................................ 4
ARGUMENT ............................................................. 7
I.

Courts Must Provide A Check On
Egregious Partisan Gerrymandering .......... 7

II.

A Justiciable Partisan
Gerrymandering Claim Requires Proof
Of Partisan Asymmetry, Lack Of
Responsiveness, And Causation ................ 10
A.

Partisan asymmetry means
there is a disparate impact on
voters based on political
affiliation. ........................................ 12

B.

Lack of responsiveness means
the ordinary political process
cannot provide a remedy ................. 14

C.

Causation means that the
partisan asymmetry is a result
of invidious discrimination, not
neutral factors or chance................. 18

 ii
III.

The Court Has Never Before
Confronted Reliable Evidence Of
These Three Discrete Elements ................. 22
A.

Bandemer, Vieth, and LULAC
did not consider evidence of
partisan asymmetry, lack of
responsiveness, and causation. ....... 23

B.

The analytical tools for
evaluating these three elements
have dramatically improved
since Bandemer, Vieth, and
LULAC ............................................. 26

CONCLUSION ........................................................ 32

 iii
TABLE OF AUTHORITIES
Page(s)
Cases
Abrams v. Johnson,
521 U.S. 74 (1997)..................................................3
Ariz. State Legislature v. Ariz. Indep.
Redistricting Comm’n,
135 S. Ct. 2652 (2015)............................................3
Badham v. Eu,
694 F. Supp. 664 (N.D. Cal. 1988).........................2
Baldus v. Members of Wisc. Gov’t
Accountability Bd.,
849 F. Supp. 2d 840
(E.D. Wisc. 2012)....................................................4
Bartlett v. Strickland,
556 U.S. 1 (2009)..................................................22
Brown v. Thomson,
462 U.S. 835 (1983)..............................................22
Bush v. Vera,
517 U.S. 952 (1996)................................................3
Cox v. Larios,
542 U.S. 947 (2004)................................................4
Davis v. Bandemer,
478 U.S. 109 (1986)...... 2, 3, 7, 8, 13, 16, 23, 24, 29

 iv
Gaffney v. Cummings,
412 U.S. 735 (1973)..............................................18
Georgia v. Ashcroft,
539 U.S. 461 (2003)................................................3
Holder v. Hall,
512 U.S. 874 (1994)................................................3
Johnson v. De Grandy,
512 U.S. 997 (1994)................................................3
League of United Latin American
Citizens (LULAC) v. Perry,
548 U.S. 399 (2006)............ 3, 21, 23, 25, 26, 28, 29
Miller v. Johnson,
515 U.S. 900 (1995)................................................3
Page v. Va. State Bd. of Elections,
No. 3:13-CV-678, 2015 WL 3604029
(E.D. Va. June 5, 2015) ..........................................3
Shaw v. Hunt,
517 U.S. 899 (1996)................................................3
Shaw v. Reno,
509 U.S. 630 (1993)................................................3
Shelby County, Alabma v. Holder,
133 S. Ct. 2612 (2013)............................................3
Thornburg v. Gingles,
478 U.S. 30 (1986)..................................................3

 v
Vieth v. Jubelirer,
541 U.S. 267 (2004)...................................... passim
Other Authorities
Amici Br. of Prof. Gary King et al.,
League of United Latin American
Citizens (LULAC) v. Perry, Nos. 5204, 5-254, 5-276, 5-439, 2006 WL
53994 (U.S. Jan. 10, 2006)...................................26
Amicus Br. of Samuel S. Wang,
Harris v. Ariz. Indep.
Redistricting Comm’n,
No. 14-232, 2015 WL 6774017
(U.S. Nov. 2, 2015) ...............................................27
Charles S. Bullock, III, & Ronald Keith
Gaddie, The Triumph of Voting
Rights in the South (2009) ...............................2, 19
Charles S. Bullock, III, Ronald Keith
Gaddie, & Justin J. Wert, The Rise
and Fall of the Voting Rights Act
(2016) ......................................................................1
Jowei Chen, The Impact of Political Geography on Wisconsin Redistricting:
An Analysis of Wisconsin’s Act 43
Assembly Districting Plan,
Election L.J. (forthcoming 2017),
https://tinyurl.com/y7ohowmy .............................31

 vi
Jowei Chen & Jonathan Rodden,
Cutting Through the Thicket:
Redistricting Simulations and the
Detection of Partisan Gerrymanders,
14 Election L.J. 312 (2015) ...................... 19, 21, 30
Wendy Tam Cho et al., A Reasonable
Bias Approach to Gerrymandering:
Using Automated Plan Generation to
Evaluate Redistricting Proposals, 59
William & Mary L. Rev. (forthcoming 2017)...............................................................31
Ronald Keith Gaddie & Charles S.
Bullock, III, Elections to Open Seats
in the U.S. House: Where the Action
Is (2000)..................................................................2
Ronald Keith Gaddie & Charles S.
Bullock, III, From Ashcroft To
Larios: Recent Redistricting Lessons
from Georgia,
34 Fordham Urb. L.J. 997 (2007) ..........................2
Bernard Grofman, Criteria for
Districting: A Social Science
Perspective,
33 UCLA L. Rev. 77 (1985) ............................20, 24
Bernard Grofman, Measures of Bias
and Proportionality in
Seats-Votes Relationships,
9 Pol. Methodology 295 (1983) ..............................1

 vii
Bernard Grofman & Thomas L. Brunell,
The Art of the Dummymander: The
Impact of Recent Redistrictings on
the Partisan Makeup of Southern
House Seats 183 (Peter Galderisi ed.,
2005) .....................................................................16
Bernard Grofman & Gary King, The
Future of Partisan Symmetry as a
Judicial Test for Partisan
Gerrymandering after
LULAC v. Perry,
6 Election L.J. 2 (2007) ............ 1, 12, 13, 14, 17, 18
Bernard Grofman, William Koetzle &
Thomas Brunell, An Integrated
Perspective on the Three Potential
Sources of Partisan Bias:
Malapportionment, Turnout
Differences, and the Geographic
Distribution of Party Vote Shares,
6 Electoral Stud. 457 (1997) ..................................1
Bernard Grofman, Michael Migalski &
Nicholas Noviello, The “Totality of
Circumstances Test” in Section 2 of
the 1982 Extension of the Voting
Rights Act: A Social Science
Perspective, 7 L. & Pol’y 199 (1985) ......................1
Samuel Issacharoff & Jonathan Nagler,
Protected from Politics: Diminishing
Margins of Electoral Competition in
U.S. Congressional Elections,
68 Ohio St. L.J. 1121 (2007) ................................17

 viii
Joint Appendix, League of United Latin
American Citizens v. Perry (LULAC),
Nos. 05-204, 05-254, 05-276, 05-439,
2006 WL 64437 (U.S. Jan. 10. 2006) .............25, 29
Justin Levitt, Where Are The Lines
Drawn?, All About Redistricting,
https://tinyurl.com/aw3qgn5
(last visited Aug. 10, 2017) .................................20
Jonathan Mattingly et al.,
Quantifying Gerrymandering,
https://tinyurl.com/yc4cvxkg (last
visited Aug. 10, 2017) ..........................................31
Michael D. McDonald & Robin E. Best,
Unfair Partisan Gerrymanders in
Politics and Law: A Diagnostic
Applied to Six Cases,
14 Election L.J. 312 (2015) ...................... 15, 19, 27
Anthony J. McGann et al.,
Gerrymandering in America
(2016) .................................. 9, 14, 15, 16, 17, 20, 27
Nat’l Conference of State Legislatures,
State Partisan Composition,
https://tinyurl.com/guos34u (last
updated Aug. 1, 2017) ............................................9

 ix
Richard G. Niemi, Bernard Grofman,
Carl Carlucci & Thomas Hofeller,
Measuring Compactness and the
Role of a Compactness Standard in a
Test for Partisan and Racial
Gerrymandering,
52 J. of Pol. 1155 (1990).........................................1
Guillermo Owen & Bernard Grofman,
Optimal Partisan Gerrymandering,
7 Pol. Geography Q. 5 (1988) .................................1
Pew Research Center, Political
Polarization in the American Public,
https://tinyurl.com/p4scahz (last
updated June 12, 2014) .......................................17
Proportional Representation, Encyclopedia Britannica (2013 ed.),
https://tinyurl.com/y6welcph ...............................13
Nicholas O. Stephanopoulos & Eric M.
McGhee, Partisan Gerrymandering
and the Efficiency Gap,
82 U. Chi. L. Rev. 831 (2015) ........................15, 28
Samuel S. H. Wang, Three Practical
Tests for Gerrymandering:
Application to Maryland and
Wisconsin, 16 Election L.J. 367
(2016) ........................................................ 13, 19, 27
Wis. State Assembly Rules
(Feb. 8, 2017),
https://tinyurl.com/y8rudrg6 .................................8

 x
Wis. State Senate Rules
(Jan. 17, 2017),
https://tinyurl.com/y8rudrg6 .................................8

 INTERESTS OF AMICI CURIAE1
Amici are political scientists who specialize in redistricting, including the statistical methods used to
detect and measure partisan gerrymandering. Amici
have served as expert witnesses and consultants in
redistricting cases on behalf of both states and plaintiffs, Republicans and Democrats. They have also
published many peer-reviewed articles on the subject.2

1 The parties have consented to the filing of this amicus
brief. No counsel for a party authored the brief in whole or in
part. No party, counsel for a party, or any person other than
amici and their counsel made a monetary contribution intended
to fund the preparation or submission of the brief.

Professor Grofman’s publications include Bernard
Grofman & Gary King, The Future of Partisan Symmetry as a
Judicial Test for Partisan Gerrymandering after LULAC v.
Perry, 6 Election L.J. 2 (2007); Bernard Grofman, William
Koetzle & Thomas Brunell, An Integrated Perspective on the
Three Potential Sources of Partisan Bias: Malapportionment,
Turnout Differences, and the Geographic Distribution of Party
Vote Shares, 16 Electoral Stud. 457 (1997); Richard G. Niemi,
Bernard Grofman, Carl Carlucci & Thomas Hofeller, Measuring
Compactness and the Role of a Compactness Standard in a Test
for Partisan and Racial Gerrymandering, 52 J. of Pol. 1155
(1990); Guillermo Owen & Bernard Grofman, Optimal Partisan
Gerrymandering, 7 Pol. Geography Q. 5 (1988); Bernard
Grofman, Michael Migalski & Nicholas Noviello, The “Totality of
Circumstances Test” in Section 2 of the 1982 Extension of the Voting Rights Act: A Social Science Perspective, 7 L. & Pol’y 199
(1985); Bernard Grofman, Measures of Bias and Proportionality
in Seats-Votes Relationships, 9 Pol. Methodology 295 (1983).
2

Professor Gaddie’s publications include Charles S. Bullock, III, Ronald Keith Gaddie, & Justin J. Wert, The Rise and

 2
Amici seek to assist the Court in understanding
recent developments in social science methodologies
for identifying and measuring the extent of partisan
gerrymanders. They do not take a position on
whether, given the particular facts and expert witness analysis, the district court correctly decided this
case. But amici firmly believe that partisan gerrymanders are justiciable, and that this Court should
adopt an articulable standard for adjudicating partisan gerrymandering claims. Social science tools now
allow courts to diagnose partisan gerrymanders with
accuracy and precision. They also allow courts to distinguish ordinary, acceptable politicking from conduct that rises to the level of unconstitutional
discrimination against voters based on their political
views. If the Court again declines to adopt a standard
for unconstitutional partisan gerrymandering, politicians will have free rein to violate associational and
representational rights.
Amicus Bernard Grofman is the Jack W. Peltason
Chair of Democracy Studies and Professor of Political
Science at the University of California, Irvine. He has
frequently served as an expert witness and consultant
in redistricting cases, including for the State of Indiana in Davis v. Bandemer, 478 U.S. 109 (1986), and
Fall of the Voting Rights Act (2016); Charles S. Bullock, III, &
Ronald Keith Gaddie, The Triumph of Voting Rights in the South
(2009); Ronald Keith Gaddie & Charles S. Bullock, III, From
Ashcroft To Larios: Recent Redistricting Lessons from Georgia,
34 Fordham Urb. L.J. 997 (2007); Ronald Keith Gaddie &
Charles S. Bullock, III, Elections to Open Seats In The U.S.
House: Where the Action Is (2000).

 3
for the plaintiffs in Badham v. Eu, 694 F. Supp. 664
(N.D. Cal. 1988), aff’d, 488 U.S. 1024 (1989). He joined
amicus briefs on behalf of neither party in Vieth v. Jubelirer, 541 U.S. 267 (2004), and League of United
Latin American Citizens (LULAC) v. Perry, 548 U.S.
399 (2006), arguing that partisan gerrymanders are
justiciable. The Court has previously cited Professor
Grofman’s work (including volumes he edited) in over
a dozen cases,3 and scholars often credit his brief in
LULAC with introducing the Court to the first generation of social science analysis of partisan asymmetry.
Professor Grofman has also drawn redistricting
plans for federal district courts, non-partisan commissions, and the U.S. Department of Justice—most recently, as the Special Master appointed by a threejudge court after it declared Virginia’s Congressional
District 3 unconstitutional. Page v. Va. State Bd. of
Elections, No. 3:13-CV-678, 2015 WL 3604029, at *18
(E.D. Va. June 5, 2015), appeal dismissed sub nom.
Wittman v. Personhuballah, 136 S. Ct. 1732 (2016).
Professor Grofman’s curriculum vitae is available at
https://tinyurl.com/y8ppxmvg.

3 See Ariz. State Legislature v. Ariz. Indep. Redistricting
Comm’n, 135 S. Ct. 2652 (2015); Shelby County, Alabama v.
Holder, 133 S. Ct. 2612 (2013); LULAC v. Perry, 548 U.S. 399
(2006); Vieth v. Jubelirer, 541 U.S. 267 (2004); Georgia v. Ashcroft, 539 U.S. 461 (2003); Abrams v. Johnson, 521 U.S. 74
(1997); Shaw v. Hunt, 517 U.S. 899 (1996); Bush v. Vera, 517
U.S. 952 (1996); Miller v. Johnson, 515 U.S. 900 (1995); Johnson
v. De Grandy, 512 U.S. 997 (1994); Holder v. Hall, 512 U.S. 874
(1994); Shaw v. Reno, 509 U.S. 630 (1993); Thornburg v. Gingles,
478 U.S. 30 (1986); Davis v. Bandemer, 478 U.S. 109 (1986).

 4
Amicus Ronald Keith Gaddie is the President’s
Associates Presidential Professor and Chair of the Department of Political Science at the University of Oklahoma and an editor of Social Science Quarterly. He
too has served as an expert witness and consultant in
numerous redistricting cases, including for the State
of Texas in LULAC and for the plaintiffs in Cox v. Larios, 542 U.S. 947 (2004). Most recently, Professor Gaddie worked as a consultant to the Wisconsin
legislature’s Republican leadership in drafting Act 43,
the map at issue in this case. As the district court explained, the Republican Caucus’s attorneys hired Professor Gaddie to assess, among other things, the
expected partisan impact of the proposed maps. J.S.
App. 12a-14a, 41a-42a, 127a, 131a, 135a, 138a-39a.
Professor Gaddie also testified in defense of the map
in the prior Voting Rights Act challenge, Baldus v.
Members of Wisconsin Government Accountability
Board, 849 F. Supp. 2d 840 (E.D. Wisc. 2012). He did
not, however, defend the map’s constitutionality in
this litigation. He has always believed that partisan
gerrymanders are justiciable. His curriculum vitae is
available at https://tinyurl.com/ya62povt.
INTRODUCTION AND SUMMARY OF
ARGUMENT
Modern, computer-driven redistricting now allows the political party in power to craft extremely sophisticated partisan gerrymanders. With vastly
improved computer speed, memory, and storage, map
drawers can design district lines so precisely that
they simultaneously maximize their party’s gains and
eliminate most competitive districts—ensuring that
the party in power enjoys an electoral advantage that

 5
endures throughout the following decade, irrespective
of voters’ subsequent choices.
Left unchecked, partisan gerrymandering fundamentally undermines our democracy. It is a basic
tenet of fair elections that the parties must play by
the same rules. But a partisan gerrymander violates
that core principle: Under a successful partisan gerrymander, one party needs fewer votes to win representation than the other party. A partisan
gerrymander places unequal burdens on voters’ opportunity to elect their representatives, based on the
party with which they associate. And where the partisan gerrymander is unresponsive to electoral shifts,
only the courts can provide a remedy.
This Court should hold that partisan gerrymandering claims are justiciable. To be precise, partisan
gerrymandering occurs when a districting plan penalizes the minority in its ability to translate its voting
support into seats compared to what might be expected from a plan drawn on the basis of neutral principles. But not all partisan gerrymanders are
unconstitutional. The Court should adopt a test for
unconstitutional partisan gerrymandering that requires a showing of three specific elements: partisan
asymmetry, lack of responsiveness, and causation.
The first element, partisan asymmetry, is based
on the idea that a citizen’s representational rights
must not depend on the party with which he chooses
to affiliate. Unlike a claim that the plaintiff is entitled
to a specified number of seats, an asymmetry standard requires only that the parties and their supporters receive equal treatment—that they have like

 6
opportunity to translate their votes into representation. Thus, if Party A would garner, say, 60% of the
seats when it wins 53% of the votes, Party B should
also garner about 60% of the seats when it wins 53%
of the votes. If it would not, partisan asymmetry is
present. The second element, lack of responsiveness,
screens out cases where the political process can provide a remedy. It examines whether a map is responsive to shifts in voters’ allegiances, such that any
disparate effect on voters is unlikely to persist
throughout the decade following redistricting. If a
map is responsive, then when voters change their allegiances, their representation also changes, making
judicial intervention unnecessary. If a map is not responsive, the courts may step in. The third element,
causation, requires that, to be actionable, a disparate
effect on voters must be the result of invidious, intentional discrimination against disfavored voters—and
not merely the natural byproduct of ordinary districting practices or chance.4
These three elements are derived from the Court’s
Equal Protection and First Amendment jurisprudence, and the social sciences offer tools for measuring each. Because each of these elements reflects a
different concept, it is important to recognize that no
one number tells it all. Rather, the Court should adopt
a test for partisan gerrymandering that makes each
4 Intent can also be proven through non-statistical evidence—for example, legislators’ own statements about their motives; departures from traditional districting criteria, such as
irregular-shaped districts; and process considerations like secrecy, limited debate, or party-line voting in the enactment of the
map. We focus here on the applicable social science evidence.

 7
of these three elements a necessary, but not sufficient,
condition of a claim.
In none of the Court’s prior partisan gerrymandering cases did the plaintiffs propose such a test,
much less offer evidence of all three elements. And the
statistical tools for detecting and measuring partisan
gerrymanders have improved greatly since the Court
last considered partisan gerrymandering in LULAC.
Courts—assisted by competent experts—can now reliably and accurately identify and measure the impact
of partisan gerrymanders, including determining
whether invidious discrimination is the cause of any
disparate burden on one political party, or whether
any disadvantage results instead from permissible,
neutral factors or random chance. The courts can, and
should, play a role in policing improper partisan gerrymanders.
ARGUMENT
I.

Courts Must Provide A Check On Egregious
Partisan Gerrymandering.

Invidious partisan gerrymandering occurs when a
political party intentionally redraws legislative district lines to give itself a durable electoral advantage
over the party out of power—usually by “packing” voters who affiliate with the opposing party into a few
safe districts, or by “cracking” them across multiple
districts to dilute their voting power. See Bandemer,
478 U.S. at 117 n.6 (explaining “the familiar techniques of political gerrymandering”). In so doing, a
partisan gerrymander discriminates against voters in
their representational rights because of their views

 8
and political associations in a way that cannot realistically be ameliorated through the ordinary electoral
process. See Vieth, 541 U.S. at 314 (opinion of Kennedy, J.) (“First Amendment concerns arise where a
State enacts a law that has the purpose and effect of
subjecting a group of voters or their party to disfavored treatment by reason of their views. In the context of partisan gerrymandering, that means … where
an apportionment has the purpose and effect of burdening a group of voters’ representational rights.”)
(opinion of Kennedy, J.); Bandemer, 478 U.S. at 124
(“[E]ach political group in a State should have the
same chance to elect representatives of its choice as
any other political group.”).
This discrimination in representational rights
has real-world consequences. A voter who supports a
disfavored party is denied an equal opportunity to use
her vote to affect the representation of her district, as
well as the partisan composition of the legislature as
a whole. And the composition of the legislature carries
high stakes. In states using a caucus system, the
party holding the majority of a chamber’s seats controls all aspects of the legislative agenda—from what
bills will see the light of day to the budget, procedural
rules, committee assignments, and so forth. See, e.g.,
J.S. App. 7a-9a, 106a; Wis. State Assembly Rules
(Feb. 8, 2017); Wis. State Senate Rules (Jan. 17,
2017). Available at https://tinyurl.com/y8rudrg6. Indeed, even in states where the majority party has less
formal agenda-setting power, the partisan makeup of
the legislature directly impacts the legislation that is
introduced, debated, and passed.

 9
There is compelling evidence that the 2010 redistricting cycle yielded partisan gerrymandering of a
magnitude that is qualitatively and quantitatively
different from what we have seen in the past—as
much as three times more partisan bias than in the
2000 redistricting cycle—even when controlling for
residential patterns of voters and demographic
change. Anthony J. McGann et al., Gerrymandering
in America 4-5, 97-98 (2016). Indeed, there were
strong increases in bias even where the same party
controlled both the 2000 and 2010 redistricting processes. Id. at 174. This increase in the aggressiveness
of partisan gerrymanders may be driven in part by
the fact that, as a result of the Court’s “signal[] in Vieth v. Jubelirer (2004) that it would not intervene …[,]
state legislatures did not have to worry about the
threat of legal oversight and pushed partisan advantage to its limits” during the 2010 cycle. Id. Absent
a judicial check, the level of egregious partisan gerrymandering may worsen still in 2020 because of a
marked increase in the number of legislatures under
unified partisan control. See Nat’l Conference of State
Legislatures, State Partisan Composition, https://tinyurl.com/guos34u (last updated Aug. 1, 2017).
Whether courts should police egregious partisan
gerrymanders is not a matter of one’s political leanings. While evidence suggests that at a national level,
the net benefits of partisan gerrymandering currently
accrue to Republicans, in the past, the benefits have
accrued to Democrats. McGann et al., supra, at 71-72,
88. Whichever party is in power has strong incentives
to change the map to keep itself there. In either case,
it is the voters who lose: Their associational and representational rights are undermined based upon their

 10
political views, and incumbents are entrenched in office without regard to changes in voter preferences.
The courts must serve as a neutral check. If the
Court again declines to adopt a standard for unconstitutional partisan gerrymandering, politicians will
have free rein to wield the technological advances we
discuss below to craft ever more egregious partisan
gerrymanders. Continued judicial abdication would
ensure only that our representatives are selected by
the self-dealing maps they enact, rather than elected
by the people they ostensibly serve—freezing into
place for a decade electoral advantages that are, for
all practical purposes, impervious to changes by the
electorate.
II. A Justiciable Partisan Gerrymandering
Claim
Requires
Proof
Of
Partisan
Asymmetry, Lack Of Responsiveness, And
Causation.
Social science now provides tools for determining
whether voters have been subjected to durable disparate treatment—as well as for measuring the precise
magnitude of any such disparity and for ruling out
neutral causes. These tools enable courts to differentiate between disparate burdens on representational
rights that are merely incidental to ordinary districting processes, and those that are the result of intentional discrimination against disfavored voters.
There is consensus among social scientists that
three discrete concepts are critical to detecting and
measuring the extent of an unconstitutional partisan

 11
gerrymander: (1) partisan asymmetry, (2) lack of responsiveness of electoral outcomes to changes in voter
decisions, and (3) causation. The Court should adopt
a test for unconstitutional partisan gerrymanders
that makes proof of each of these elements necessary
for a claim. Together, these elements—which, although independently derived, largely parallel the
standard proposed by the plaintiffs here—are key to
demonstrating that voters have suffered disparate
and durable burdens on their representational rights
because of their political views and associations. They
also provide evidence as to whether any differential
treatment is intentional or instead is the result of
other, neutral factors.
This test is not based on an abstract notion of fairness akin to a requirement that seat share equal the
party’s share of the overall vote. It is a standard of
neutral treatment of the parties in allocating representational rights. And the burden on voters is measured relative to the baseline created by neutral
factors: single-member, winner-take-all elections (the
norm in the United States); compliance with federal
constitutional requirements and the Voting Rights
Act; the actual residential patterns of the electorate;
map-drawing practicalities like the need for contiguous and compact districts; and the role of random
chance. The test recognizes that map drawing inevitably has some political fallout, while giving courts a
means to distinguish and identify those egregious
partisan gerrymanders that go above and beyond to
invidiously target opposition voters for unequal treatment.

 12
The first element, partisan asymmetry, considers
whether and to what degree voters’ representational
rights have been burdened. The second, lack of responsiveness—also called “durability”—considers
whether the ordinary political process is able to provide a remedy. And the third, causation, ensures that
only invidious, intentional discrimination is actionable, as distinct from disparate effects that are merely
the result of neutral factors or chance. No one factor
is dispositive. Rather, each of these three discrete elements—partisan asymmetry, lack of responsiveness,
and causation—must be assessed separately and
should be deemed a necessary, but not sufficient, condition of a partisan gerrymandering claim.
A. Partisan asymmetry means there is a
disparate impact on voters based on
political affiliation.
The first element, partisan asymmetry, speaks to
whether there has been a clear and severe disparate
impact on a political party and its supporters. It asks
whether the map treats similarly situated parties
equally: whether both parties receive like opportunity
to capture a given number of legislative seats if they
receive a comparable share of the statewide vote.
For example, imagine that the “Democratic Party
receives an average of 55% of the vote totals in a
state’s legislative district elections and, because of the
way the district lines were drawn, it wins 70% of the
legislative seats in that state.” Bernard Grofman &
Gary King, The Future of Partisan Symmetry as a Judicial Test for Partisan Gerrymandering after LULAC
v. Perry, 6 Election L.J. 2, 8 (2007). This “one piece of

 13
evidence alone” says nothing about whether any voters have been treated differently based on their political views. Id. That turns on whether the result would
be different were the shoe on the other foot: If the Republican Party would also have received 70% of the
seats in an election in which it garnered an average
of 55% of the vote, then there is no disparate treatment. Id.
Critically, as the foregoing example indicates, a
symmetry standard is not equivalent to a proportionality standard, which this Court has rightly rejected.
In a system of proportional representation (used in
many European countries), seats are awarded in proportion to overall vote share—i.e., 30% of the
statewide votes would garner about 30% of the legislative seats. Proportional Representation, Encyclopedia
Britannica
(2013
ed.),
available
at
https://tinyurl.com/y6welcph. Supreme Court precedents “clearly foreclose any claim that the Constitution
requires
proportional
representation.”
Bandemer, 478 U.S. at 130 (opinion of White, J.).
Nor does mere disproportionality evidence a partisan gerrymander. The political science is clear: Winner-take-all, single-member district elections—
elections in which a plurality of the votes wins the district’s seat—do not produce proportionate results, because “in practice they normally give a ‘bonus’ of
varying sizes (above proportionality) in seats to the
party that wins a majority of the votes across a state.”
See Grofman & King, The Future of Partisan Symmetry, supra, at 9; see also, e.g., Samuel S. H. Wang,
Three Practical Tests for Gerrymandering: Application to Maryland and Wisconsin, 16 Election L.J. 367,

 14
368, 374 (2016). Thus, it is generally not possible to
directly infer asymmetry from disproportionality. See
McGann et al., supra, at 65-66 (“[A symmetry standard] does not require proportionality but only that the
disproportionality be the same for both parties.”).
Rather than embodying a particular political theory, partisan symmetry requires only that if we were
to “switch the names of the parties that received particular vote outcomes, the seat outcomes would also
switch.” Grofman & King, The Future of Partisan
Symmetry, supra, at 8. “[I]n other words[,]” it requires
“that outcomes not depend on party names.” Id. And
measures of partisan asymmetry show not only
whether a map provides an advantage to one party
over another, but also the degree of the advantage.
The scholarly literature has uniformly supported
partisan asymmetry as the definition of disparate
partisan impact in electoral systems since at least the
late 1980s. See id. at 6 & nn.29-30 (canvassing publications on the subject). But as explained below (§ III),
until now, the concept has never been squarely presented to this Court.
B. Lack of responsiveness means the
ordinary
political
process
cannot
provide a remedy.
The second necessary element derived from social
science is lack of responsiveness. While asymmetry
shows a disparate effect on voters’ representational
rights, that alone is not enough to demonstrate an improper gerrymander. If the party out of power can alter its fate by persuading voters to support it in the

 15
next election, then there is no need for courts to intervene. Rather, ordinary politics remain responsive to
voters’ preferences, and if citizens do not like the policies promulgated by their representatives (including
the district maps they enact), they can vote them out
of office. See Michael D. McDonald & Robin E. Best,
Unfair Partisan Gerrymanders in Politics and Law: A
Diagnostic Applied to Six Cases, 14 Election L.J. 312,
319 (2015) (arguing that the Court “entered the metaphorical political thicket in the 1960s on the question of malapportionment” due to “the practical
problem … that popular majorities had no political
means to correct the offense”); Nicholas O. Stephanopoulos & Eric M. McGhee, Partisan Gerrymandering and the Efficiency Gap, 82 U. Chi. L. Rev. 831, 865
(2015) (“So long as certain plans would remain unbalanced over an array of potential outcomes … the case
for judicial intervention is unaffected.”).
Moreover, the magnitude of partisan asymmetry
and its expected duration can be unrelated. McGann
et al., supra, at 65 (“These two qualities [of asymmetry and responsiveness] are independent.”). In
principle, even large-scale disparities in treatment of
the parties can be fleeting. A constitutional standard
for partisan gerrymanders should accordingly require
a separate assessment of electoral responsiveness,
sometimes called “durability.”
Electoral responsiveness describes whether and
how representation changes when voters’ preferences
change. Based on historical data—how much voters’
preferences swung in prior elections—experts can
identify the full range of realistically possible election
outcomes (vote shares) and then determine how many

 16
legislative seats, if any, would change hands in response to a comparable change in voters’ choices. The
number of competitive districts also provides evidence
of the map’s responsiveness.
If a map is not responsive, that means that when
voters change their preferences and shift their allegiances from one party to another, their representation remains unlikely to change—showing that the
politicians have chosen the voters, and not the other
way around. In that circumstance, we can expect partisan asymmetry to endure regardless of the outcome
of future elections. Conversely, high responsiveness
suggests that the disparate effect on voters may not
be long-lasting.
Measuring responsiveness will also detect a socalled “dummymander.” Bernard Grofman & Thomas
L. Brunell, The Art of the Dummymander: The Impact
of Recent Redistrictings on the Partisan Makeup of
Southern House Seats, Redistricting in the New Millennium 183, 184 (Peter Galderisi ed., 2005). As Justice
O’Connor
noted
in
Bandemer,
some
gerrymanders could be “self-limiting,” if map drawers
crack voters across multiple districts to create margins of victory so thin that they evaporate in future
elections. Bandemer, 478 U.S. at 152 (O’Connor, J.,
concurring). But dummymanders can occur only when
there are a number of competitive districts in a map.
And there is empirical evidence that dummymanders
are rare. See McGann et al., supra, at 226 (“A second

 17
myth we have debunked is that partisan gerrymandering is self-limiting”).5 In any event, assessing responsiveness “allows us to distinguish those cases in
which a gerrymandering might have been attempted
but was not very well done from those cases in which
the partisan bias imposed by gerrymandering is expected to be both substantial and long-lasting.”
Grofman & King, The Future of Partisan Symmetry,
supra, at 13.

There are two clear explanations for why dummymanders
are so uncommon: First, the newest, computer-driven redistricting now allows map drawers to make very precise refinements
to district lines down to the census-block level. With this sophisticated new technology, map drawers can fashion maps that
eliminate meaningful competition for most districts. See
McGann et al., supra, at 87 (“[A]rmed with modern geographical
information system software and an absence of judicial constraints, it is possible to engineer so much advantage that [a map
can] satisfy both … goals” of “seat maximization and incumbent
protection.”). Thus, generally speaking, gerrymandered victory
margins are no longer so thin that they risk disappearing. See
Samuel Issacharoff & Jonathan Nagler, Protected from Politics:
Diminishing Margins of Electoral Competition in U.S. Congressional Elections, 68 Ohio St. L.J. 1121, 1122 (2007) (“[D]espite
relative overall national parity between the parties in the postWar period, the districts held by each party tend to be more
firmly in their control than ever before.”). Second, political polarization of the electorate is increasing. See Pew Research Center, Political Polarization in the American Public, available at
https://tinyurl.com/p4scahz (last updated June 12, 2014) (“Republicans and Democrats are more divided along ideological
lines—and partisan antipathy is deeper and more extensive—
than at any point in the last two decades.”). With fewer swing
voters, there is less risk of a victory margin eroding over time.
5

 18
Requiring that plaintiffs demonstrate that a disparate partisan impact will be durable throughout the
decade following redistricting—that the map is not responsive to voters—ensures that courts do not intervene in the political process when it is functioning
properly. If the map does not persistently obstruct
competition, the voters’ remedy lies at the polls, not
in the courts.6
C. Causation means that the partisan
asymmetry is a result of invidious
discrimination, not neutral factors or
chance.
Assessing partisan asymmetry and responsiveness is still not enough. There is a consensus among
social scientists that to determine whether invidious
discrimination is the cause of a disparate burden on
voters, it is necessary to rule out other potential
causes—to assess whether the partisan effects of a
plan are attributable, for example, to neutral principles, voters’ residential patterns, or sheer random
6 Conversely, that responsiveness is low is not, by itself,
enough to establish an unconstitutional partisan gerrymander.
For example, if both parties agree to apportion single-member
districts in proportion to their respective vote shares, that would
be “effectively synonymous with requiring low levels of electoral
responsiveness.” Grofman & King, The Future of Partisan Symmetry, supra, at 9. Yet there is no need for judicial intervention
when legislatures choose to apportion the state proportionately.
Gaffney v. Cummings, 412 U.S. 735, 754 (1973) (“[J]udicial interest should be at its lowest ebb when a State purports fairly to
allocate political power to the parties in accordance with their
voting strength[.]”). As with asymmetry and causation, low responsiveness is a necessary but not sufficient condition for a constitutional claim.

 19
chance. See, e.g., Wang, Three Practical Tests, supra,
at 374 (“[A] standard for partisan gerrymandering requires a method for determining whether a [claimed
disparity] could have arisen as part of normal variation in districting as practiced across the United
States.”); McDonald & Best, supra, at 317 (“[I]n order
to distinguish unintentional from intentional gerrymanders, a benchmark of what naturally would result
from any neutral line drawing has to be established.”); Jowei Chen & Jonathan Rodden, Cutting
Through the Thicket: Redistricting Simulations and
the Detection of Partisan Gerrymanders, 14 Election
L.J. 312, 332 (2015) (“[P]artisan asymmetry in the
transformation of votes to seats could happen for several reasons that cannot be traced to partisan manipulation ….”). That is, we must compare the map’s
disparate effects against a neutral baseline.
As the Court has noted, advantages to one party
may occur due to a variety of neutral factors. See, e.g.,
Vieth, 541 U.S. at 289-90 (plurality); id. at 308-09
(Kennedy, J., concurring). For example, map drawers
must comply with the Constitution’s “one-person, onevote” and non-discrimination requirements. They also
must comply with the Voting Rights Act. See Charles
S. Bullock, III, & Ronald Keith Gaddie, The Triumph
of Voting Rights in the South 343 (2009) (discussing
partisan alignment of groups protected by Voting
Rights Act). And many states’ laws also require map
drawers to take into account certain traditional districting criteria. Almost every state, for example, requires districts to be contiguous. Most also require
compact districts that do not split political subdivisions across districts. And a handful require the
preservation of communities of interest—groups of

 20
people with a common interest like race or ethnicity.
See, e.g., Justin Levitt, Where Are The Lines Drawn?,
All About Redistricting, https://tinyurl.com/aw3qgn5
(last visited Aug. 10, 2017) (collecting current, stateby-state legal requirements for redistricting); see also
Bernard Grofman, Criteria for Districting: A Social
Science Perspective, 33 UCLA L. Rev. 77 (1985) (Table
3) (collecting state-by-state requirements for 1980s
round of redistricting).
Compliance with these neutral criteria may lead
to inadvertent advantages to one party. Similarly,
there is some evidence that “political groups that tend
to cluster (as is the case with Democratic voters in cities) [c]ould be systematically affected by what might
be called a ‘natural’ packing effect,” Vieth, 541 U.S. at
290 (plurality)—although new empirical evidence indicates that this effect has been overstated. McGann
et al., supra, at 135 (“[G]eographic and demographic
constraints (such as the urban concentration of Democratic voters, the requirement to draw majority-minority districts, and the geographic sorting of voters)
cannot account for the level of partisan bias we observe and certainly cannot account for the increase in
bias we observe between the 2000 and 2010 districting rounds.”). Partisan asymmetry could also potentially occur by random chance in the map-drawing
process.
Partisan asymmetry that is merely a side effect of
indisputably legitimate objectives within the redistricting process or that is naturally occurring does not
evidence actionable invidious discrimination. Any
constitutional test for partisan gerrymandering will
thus have to rule out these causes of asymmetry and

 21
isolate the degree of asymmetry that is “unrelated to
the [legitimate] aims of apportionment,” or to residential patterns or chance. Vieth, 541 U.S. at 313 (Kennedy, J., concurring).
As explained below (§ III), there are now extremely sophisticated and accurate methods of ruling
out neutral factors as the source of partisan asymmetry. These tools enable experts to identify the precise quantum of disparate treatment that is “manmade”—the product of deliberate efforts of the party
in power to penalize the opposition—as distinct from
the level of disparity that may be produced by the effects of neutral districting priorities, voters’ residential patterns, or chance. See, e.g., Jowei Chen &
Jonathan Rodden, Cutting Through the Thicket: Redistricting Simulations and the Detection of Partisan
Gerrymanders, 14 Election L.J. 312 (2015).
***
When partisan asymmetry, lack of responsiveness, and causation are each shown, we are able to
establish the existence of discrimination against voters based on their political views and associations
that is unlikely to be remedied by the political process. Beyond that, whether courts should nonetheless
tolerate some degree of discrimination before they
will intercede is a question for judges, not social scientists. The question of “how much partisan dominance is too much,” LULAC, 548 U.S. at 420 (opinion

 22
of Kennedy, J.), is fundamentally a legal one for
courts to decide.7
III. The Court Has Never Before Confronted
Reliable Evidence Of These Three Discrete
Elements.
Social science now offers straightforward and
manageable ways to prove (or disprove) partisan
asymmetry, lack of responsiveness, and causation.
But that was not always true. The analytical tools for
evaluating each of these three elements have dramatically improved since the Court last considered the
justiciability of partisan gerrymandering in LULAC.
It is thus unsurprising that this is the first case before
this Court in which the plaintiffs offered evidence of
each of the three necessary elements. See, e.g., J.S.
7 The available social science tools are now well suited to
analyzing the kind of threshold requirements that the Court has
adopted in other election-law contexts. For example, the Court
could require the plaintiffs to establish that at least one seat now
lost to partisan gerrymandering could be gained in a neutral
plan. This is feasible because most measures of asymmetry can
be translated into a percentage of the seats in a plan affected.
Cf. Bartlett v. Strickland, 556 U.S. 1, 26 (2009) (adopting, in Voting Rights Act § 2 case, threshold requirement that plaintiffs
demonstrate a “geographically compact group of minority voters
[that] could form a majority in a single-member district”). Alternatively, the Court could set a threshold level of partisan asymmetry that triggers judicial scrutiny, using historical data to
identify the amount of asymmetry that is atypical or egregious.
Cf. Brown v. Thomson, 462 U.S. 835, 842 (1983) (“Our [one-person-one-vote] decisions have established … that a [state legislative] apportionment plan with a maximum population deviation
under 10% falls within this category of minor deviations [that
are not actionable.]”).

 23
App. 146a-66a, 173a-74a (asymmetry and responsiveness, i.e., durability), 180a-81a, 191a-196a, 197a
n.350, 200a-12a (causation, i.e., absence of justification).
A. Bandemer, Vieth, and LULAC did not
consider
evidence
of
partisan
asymmetry, lack of responsiveness, and
causation.
In the course of rejecting the plaintiffs’ claims in
Bandemer, Vieth, and LULAC, the Court hinted that
partisan asymmetry, lack of responsiveness, and causation are important to a justiciable partisan gerrymandering claim. See LULAC, 548 U.S. at 418
(holding that “unconstitutional acts of partisan gerrymandering must do what appellants’ sole-motivation
theory disavows: show a burden, as measured by a reliable standard, on the complainants’ representational rights”); Vieth, 541 U.S. at 289-90 (plurality)
(holding that plaintiffs failed to establish a standard
under which they were entitled to a majority of the
seats, and that they failed to rule out “natural” causes
of packing); Bandemer, 478 U.S. at 129-130, 140
(holding that plaintiffs’ claims failed because proportionality is not required and because “more than a
showing of possibly transitory results” is required).
But in none of those cases did the plaintiffs (or the
Justices) propose a test based on these elements, and
the plaintiffs never provided evidence of these elements to the Court. Indeed, the first and only time the
Court addressed partisan asymmetry was in LULAC,
where only an amicus brief (which Professor Grofman
joined), and not the parties, discussed the concept.

 24
Contrary to the Whitford defendants’ contention
that the evidence in this case is equivalent to that rejected in Bandemer (Brief for Appellants 39), the primary evidence in Bandemer was that a single election
had yielded slightly disproportionate results. 478 U.S.
at 134 (plurality). The Bandemer plaintiffs offered no
evidence of partisan asymmetry, lack of responsiveness, or causation. Instead of partisan asymmetry,
they offered proportionality. But as Professor
Grofman—Indiana’s expert witness in that case—explained, it is “totally fallacious … that a discrepancy
between vote share and seat share of more than a few
percentage points is proof of intentional gerrymandering.” Grofman, Criteria for Districting, supra, at
120. Nor did the plaintiffs there offer any evidence of
lack of responsiveness, leaving unrebutted the State’s
contention that if the plaintiffs won even an “additional few percentage points …, they would have obtained a majority … in both houses.” Bandemer, 478
U.S. at 135 (plurality). Finally, plaintiffs failed to
prove causation because their test left unaddressed
discrepancies in treatment caused merely by “natural
advantages.” Grofman, Criteria for Districting, supra,
at 120.
In Vieth, the plaintiffs took a somewhat different
tack. They argued for a two-pronged test: (1) a predominant intent to achieve partisan advantage,
shown through the subordination of neutral and legitimate criteria (i.e., intent); and (2) a “totality of the
circumstances” determination that the map could
“thwart the plaintiffs’ ability to translate a majority
of votes into a majority of seats,” (i.e., effect). 541 U.S.
at 284-87 (plurality).

 25
The effects prong of this test focused on the wrong
criteria: It claimed that a party that won the majority
of votes was entitled to a majority of seats, without
establishing any differential treatment of voters
based on their political views and associations. Specifically, because the case was decided on a motion to
dismiss, and because no election had taken place under the challenged plan, the plaintiffs’ claim of adverse effects rested solely on an allegation that, in the
future, they would be deprived of a majority of Pennsylvania’s congressional seats, despite achieving a
majority of the statewide vote. Id. at 272-73, 287. The
plurality noted that this claim reduced to a claim of
proportional representation, similar to the proportionality test urged in Bandemer. Id. at 288. And of
course, there was no evidence of partisan asymmetry,
responsiveness, or causation.
In LULAC, the district court heard limited expert
evidence regarding partisan asymmetry and responsiveness, including testimony from Professor Gaddie—namely, a measure of “partisan bias” that
examined how many seats each party would win if,
hypothetically, each obtained 50% of the statewide
vote. 548 U.S. at 466-68 (Stevens, J., concurring in
part and dissenting in part). See also J.A., League of
United Latin American Citizens v. Perry (LULAC),
Nos. 05-204, 05-254, 05-276, 05-439 2006 WL 64437,
at *36-37 (U.S. Jan. 10. 2006) (report of Professor
John R. Alford, expert for plaintiffs); id. at *216 (report of Professor Gaddie, expert for the State).
But, plaintiffs abandoned this evidence by the
time they got to this Court. Instead, their theory of

 26
the case was that the sole motive for the Texas legislature’s decision to engage in mid-decennial redistricting was to reap partisan advantage. Id. at 416-17
(opinion of Kennedy, J.). In other words, their theory
depended only on intent. In fact, they argued that
“courts need not inquire about, nor parties prove, the
discriminatory effects of partisan gerrymandering.”
Id. at 417 (emphasis added). Professor Grofman
raised the concept of partisan asymmetry as relevant
to discriminatory effect in his amicus brief, but the
parties did not squarely present the issue. See Amici
Br. of Prof. Gary King et al., League of United Latin
American Citizens v. Perry (LULAC), Nos. 5-204, 5254, 5-276, 5-439, 2006 WL 53994 (U.S., Jan. 10,
2006).
B. The analytical tools for evaluating these
three elements have dramatically
improved since Bandemer, Vieth, and
LULAC.
The analytical tools for evaluating partisan asymmetry, lack of responsiveness, and causation have
also dramatically improved since Bandemer, Vieth,
and LULAC.
In LULAC, Justice Kennedy expressed concern
that the measure of “partisan bias” that examined
how many seats each party would win if it obtained
50% of the statewide vote relied on “a hypothetical
state of affairs.” Id. at 420 (opinion of Kennedy, J.).
The test of partisan asymmetry that we propose does
not involve predictions about who will win future elections. Instead, if the “Democratic Party receives an
average of 55% of the vote totals in a state’s legislative

 27
district elections and, because of the way the district
lines were drawn, it wins 70% of the legislative seats
in that state,” our test asks whether the result would
be different were the shoe on the other foot: If the Republican Party would also have received about 70% of
the seats in an election in which it garnered an average of 55% of the vote. Supra, at 12-13. In any event,
in cases like this one where multiple elections have
occurred under the challenged plan, the accuracy of
the seats-votes graph used to calculate the magnitude
of any partisan asymmetry can be directly confirmed.
Moreover, new measures of asymmetry developed
after LULAC rely on no “hypothetical” counterfactual
at all. For example, the average-median difference is
“a simple measure of asymmetry or skewness …
[with] well-defined mathematical properties.” Wang,
Three Practical Tests, supra, at 372. The average-median difference compares each party’s actual vote
share in its median district to its average actual vote
share across all districts. If the party’s median vote
share is significantly lower than its average vote
share, partisan asymmetry is at work. This is because
“[b]y packing opposing voters into a small number of
districts, the gerrymandering party holds down the
targeted party’s vote shares in many districts, which
depresses the target party’s median vote share, even
while its average (mean) vote share is unchanged.”
Amicus Br. of Samuel S. Wang, Harris v. Ariz. Indep.
Redistricting Comm’n, No. 14-232, 2015 WL 6774017,
at *4 (U.S. Nov. 2, 2015). The average-median difference is also highly manageable for courts: “[i]t focuses
on two observable numerical facts”—the mean and
the median—“and subtracts one from the other.”
McDonald & Best, supra, at 316. This is the first case

 28
in which the plaintiffs have presented evidence of the
average-median difference. See Mot. to Affirm at 12
n.4, 21 n.8.
The plaintiffs here have also made use of another,
easy-to-calculate measure that analyzes actual election results—the efficiency gap. See J.S. App. 159a66a. The efficiency gap is intended to address partisan asymmetry, in that it compares how many votes
each party respectively “wasted” in a given election—
the votes each party received that did not contribute
to it winning an additional seat. Stephanopoulos &
McGhee, supra, at 849-50.8 Like the average-median
difference, the efficiency gap is a social science tool
never before presented to the Court.
In LULAC, Justice Kennedy also explained that
“asymmetry alone is not a reliable measure.” 548 U.S.
at 420 (opinion of Kennedy, J.) (emphasis added). As
explained in § II, we agree. Although Professor
Grofman’s amicus brief in LULAC focused on the relevance of asymmetry to partisan gerrymandering

8 In this case, the plaintiffs also used the efficiency gap as a
measure of responsiveness. They presented evidence regarding
Act 43’s efficiency gap in the elections following adoption of the
map. J.S. App. 50a. They also presented a historical analysis
suggesting that when a map exhibits an efficiency gap of a sufficiently large magnitude in the first election following its adoption (7% or more), the map is likely to continue to exhibit an
efficiency gap in favor of that party for the rest of the decade. Id.
48a-50a. And they presented evidence of how Act 43’s efficiency
gap would change if citizens shifted their votes in accordance
with historical patterns of vote shifts in Wisconsin. Id. 47a-48a.

 29
claims, we believe a justiciable standard also requires
proof of lack of responsiveness and causation.
As with asymmetry, given the evidence available
to the district court, there is no need here to rely on
any kind of predictions to assess responsiveness. Responsiveness can be observed directly based on election outcomes under the challenged map. In contrast,
in each of the Court’s prior partisan gerrymandering
cases, only one election or no election had occurred
under the challenged plan. See LULAC, 548 U.S. at
413 (opinion of Kennedy, J.) (one); Vieth, 541 U.S. at
272 (plurality) (none); Bandemer, 478 U.S. at 115
(plurality) (one). We continue to believe that experts
can reliably assess the responsiveness and asymmetry of a newly enacted map by projecting the results of recent past statewide races onto the new
district lines, especially in light of current extraordinarily high levels of partisan polarization. See supra
note 5. But, when multiple elections under the challenged map have already occurred—in the instant
case, there have been three—there is no need for such
projections. Courts and expert witnesses can analyze
actual election results for any disparate and durable
effects on disfavored voters.
As to causation—or the absence of any neutral
justification—the only evidence of causation in LULAC involved comparing the challenged plan to the
prior map. There was no evidence isolating the degree
of asymmetry that occurred from neutral redistricting
criteria or chance. LULAC, 548 U.S. at 451-52 (Stevens, J., concurring in part and dissenting in part);
see also J.A., LULAC, 2006 WL 64437, at *36-39 (report of Professor John R. Alford, expert for plaintiffs);

 30
id. at *224-25 (testimony of Professor Gaddie, expert
for the State).
Now, not only are traditional tests of statistical
significance available for partisan asymmetry, vastly
improved computing power permits experts to create
thousands (or even many millions) of computer-generated alternative maps. These can then be screened
to consider only those plans that satisfy all standard
districting criteria to at least the same extent as the
challenged plan, establishing the neutral benchmark
against which to measure the magnitude of “manmade” asymmetry in the treatment of different blocs
of voters. Using these alternative maps, we can say
with a high degree of statistical confidence whether a
given quantum of asymmetry is explainable by something other than invidious intent.
For example, some of the most advanced work in
the field is that of Jowei Chen and Jonathan Rodden.
They generate thousands of maps with simulated district lines that can control for “all legal criteria and
requirements in redistricting”—maps that are at
least as good as the challenged plan on all neutral criteria. Chen & Rodden, supra, at 335. By “measuring
the partisan[] [asymmetry] of these [computer-generated] plans and contrast[ing] them with that of the
plan in question,” one can determine, with a high degree of statistical confidence, the extent to which the
challenged plan exhibits asymmetry over and above
the neutral baseline. Chen & Rodden, supra, at 338.
Moreover, “[a]ny natural geographic advantage for
one party or another will be expressed in the partisanship of the simulated plans.” Id. Other scholars,
such as Professor Wendy Tam Cho, have done very

 31
similar computations, involving an even larger number of alternative maps. Wendy Tam Cho et al., A Reasonable Bias Approach to Gerrymandering: Using
Automated Plan Generation to Evaluate Redistricting
Proposals, 59 William & Mary L. Rev. (forthcoming
2017) (generating millions of alternative maps); see
also Jonathan Mattingly et al., Quantifying Gerrymandering, https://tinyurl.com/yc4cvxkg (last visited
Aug. 10, 2017) (generating 150,000 to 200,000 alternative maps for various states).
This mechanism of isolating causation was not
feasible at the time of LULAC. Now, with dramatic
improvements in computer processing speed,
memory, and storage, we can produce thousands of
maps in minutes. Notably, Professor Chen applied his
methodology to Wisconsin’s Act 43 and concluded that
the “levels of natural electoral bias pale in comparison
to the much more extreme electoral bias exhibited by
the Act 43 plan.” Jowei Chen, The Impact of Political
Geography on Wisconsin Redistricting: An Analysis of
Wisconsin’s Act 43 Assembly Districting Plan, Election L.J. (forthcoming 2017) (manuscript at 3),
https://tinyurl.com/y7ohowmy.
***
State-of-the-art analytical tools now capture all
the relevant information for detecting and precisely
measuring the disparate effect of partisan gerrymanders. In particular, the various methods of measuring
asymmetry are fundamentally complementary. Some
are more complex in their calculations than others.
But they all measure the same thing: the magnitude
of the disparate burden (if any) that a challenged map

 32
imposes on a political party and its supporters. And
they all converge in conclusions in the face of an egregious partisan gerrymander. In the rare circumstance
that one method is unsuitable to a particular context,
another can be used instead.
While the methodology will continue to improve,
future advances are likely to be incremental only—
the equivalent of adding a further decimal point to an
already precise figure—and will not materially alter
the calculus. Moreover, experts can clearly and consistently apply existing statistical tools to assess
whether each element—partisan asymmetry, lack of
responsiveness, and causation—is met. Once the
Court adopts a legal standard for justiciable partisan
gerrymandering claims, it will be relatively straightforward for competent experts to provide their assessments of whether that standard is met in a given case.
CONCLUSION
For the foregoing reasons, the Court should hold
that partisan gerrymander claims are justiciable, and
it should adopt a standard that makes partisan asymmetry, lack of responsiveness, and causation necessary elements of such a claim.

 33
Respectfully submitted,

Thomas M. Bondy
E. Joshua Rosenkranz
Avi Daniel Rosenblit
Counsel of Record
ORRICK, HERRINGTON & Rachel Wainer Apter
SUTCLIFFE LLP
Hannah Garden1152 15th Street
Monheit
Washington, DC 20005 ORRICK, HERRINGTON &
SUTCLIFFE LLP
51 West 52nd Street
New York, NY 10019
(212) 506-5000
jrosenkranz@orrick.com
August 10, 2017