Amicus Curiae Brief — Gill v. Whitford, 138 S. Ct. 52 (2017) (No. 16-1161)

FILED

AUG 30 2017

No. 16-1161 | ShPREME COURT OSS

IN THE

Supreme Court of the United States

BEVERLY R. GILL ET AL.,

Appellants,

Vv.

WILLIAM WHITFORD ET AL.,

Appellees.

On Appeal from the United States District Court for

the Western District of Wisconsin

BRIEF OF HEATHER K. GERKEN, JONATHAN

N. KATZ, GARY KING, LARRY J. SABATO, AND

SAMUEL S.-H. WANG AS AMICI CURIAE IN

SUPPORT OF APPELLEES

Kevin K. Russell Heather K. Gerken

GOLDSTEIN & Counsel of Record

RUSSELL, P.C 127 Wall Street

- ret New Haven, CT 06511

7475 Wisconsin Ave. (203) 432-1660

Suite 850 heather.k.gerken@

Washington, DC 20814 yale.edu

LAE ELI LOCATE ne a a

WiILSON-EPES PRINTING CO.,INC — (202) 789-0096 — WASHINGTON, D C 20002

II.

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TABLE OF CONTENTS

The Court’s Long-Standing Practice Is To

Identify A Workable Principle That Lends

Itself To A Manageable Test While Allowing

A. The Court Has Repeatedly Followed This

Cautious Practice In Elections Cases..........

B. This Cireumspect Approach Is Not

Limited To Elections Cases........................-.

C. Now Is The Time For The Court To Acct. .....

Partisan Symmetry Is A Workable Standard

With Ancient Roots And Overwhelming

Support From Social Scientists. .....................006.

A. Partisan Symmetry Is A Deeply [ntuitive

Standard With Ancient Roots. .....................

B. Social Scientists Resoundingly Support A

Partisan Symmetry Standard......................

Partisan Symmetry Lends Itself To A

A. Partisan Symmetry Relies On The Most

Basic Statistical Measures And Is Thus

Transparent And Easy To Calculate

Without Undue Reliance On Experts. .........

ee ee ee ee ee

CORPO THEREOF

i

12

13

14

15

18

ii

B. Partisan-Symmetry Tests Differ

Fundamentally From A _ Proportional

Representation Standard. ..................02...-0-+- 21

C. Partisan Symmetry Tests Can Distinguish

Between Partisan Manipulation And The

Effects Of Traditional Districting

IDS cscsicnndctiapmdehiinintcigshntbuiiinadaembdammbateieds 22

D. Because Symmetry Tests Do Not Rely On

Subjective Judicial Judgments, They

Generate Highly Predictable Measures

That Do Not Displace Appropriate

I . asinidiinteannnisiaines 23

E. Symmetry Tests Measure Opportunity,

Not Outcome, And Are Thus Tailored To

The Constitutional Harm At Issue. ............. 24

F. Partisan Symmetry Tests Are Flexible

And Can Be Deployed Simultaneously To

Ensure That Judges Can Identify Extreme

Outliers And Be Confident In The

Robustness Of Their Findings. .................... 25

IV. Wisconsin’s Legislative Districts Would Fail

Under Virtually Any Partisan-Symmetry Test

The Court Might Choose. ................::s0sesseeereeeeeees 26

IIIT Ui vciniinintactomiedeaboddipeedinninnianinioiouiaanansgsaie 28

TABLE OF AUTHORITIES

Cases

Avery uv. Midland Cty.,

ET ee eee en aN 8

Baker v. Carr,

TEN RM Te SEERA MEER > 6, 7

Bartlett v. Strickland,

SIE TTT ii iciccndcnnptiennenbiebessnsneborinnéenenetionsind 9

Bazemore v. Friday,

478 U.S. 385 (1986) (per curiam).................... 14,19

Brown v. Bd. of Educ.,

ESET nee me 7,10

Burdick v. Takushi,

AE RR RE aR eS 7

Bush v. Vera,

I ccunuunns 10, 23

California Democratic Party v. Jones,

Ee a ae 7

Campos v. City of Baytown,

840 F.2d 1240 (5th Cir. 1988)................0.ccc cece )

Castaneda v. Partida,

TI ne aT ae ee are ee 19

Citizens United v. FEC,

a sesmmannoenatnmnenennns 6

Covington v. North Carolina,

316 F.R.D. 117 (M.D.N.C. 2016), aff'd, 137 S.

as cdnheenaccecornuncsenes 10

Crawford v. Marion Cty. Election Bd.,

ERT RE a N 7

Davis v. Bandemer,

I canil 23

iv

FTC v. Actavis, Inc.,

TER I Re ee EE 11

General Elec. Co. v. Joiner,

I scaies anibecnas 19

Global-Tech Appliances, Inc. v. SEB S.A.,

dos iientcintsatedemsinbesuvaiedhaseosoeceues 11

Green v. Cty. Sch. Bd.,

sel datidiiestibnanesninn 10

Grutter v. Bollinger,

at sarsrrccsemibdinsnbainnebenduntaisoues 7

Harris v. Forklift Systems, Inc.,

Nees casnstnrncaomietnnsata 11

Havens Realty Corp. v. Coleman,

ETT io cerccenenianscndeséneesanseueseneusooutaces 15

Johnson v. De Grandy,

eo cnseunsinnidiasbontmeiie 9

Karcher v. Daggett,

TIE CS SPST 8, 21

Keyes v. Sch. Dist. No. 1,

413 U.S. 189 (1973)..................... Ral el eas a 10

Kirkpatrick v. Preisler,

I 1s scccnncsenanntenchosonebeoenatensnsscosoost 8

League of United Latin Am. Citizens (LULAC) v.

Perry,

I ccaensenonsle passim

League of United Latin Am. Citizens v.

Clements,

999 F.2d 831 (Sth Cir. 1993).............cccccccccrrseeecossees )

Loving v. Virginia,

EID SNE econ emer ew 7

Mahan v. Howell,

EERE RL EN 8

Maslenjak v. United States,

I IT. cncrnsrndneinonscosecooonccennee 5,12

Matrixx Initiatives, Inc. v. Siracusano,

a ondtnaneiaiiotusantieimavio 19

McConnell v. FEC,

ET ES Ns ann me Sa 6,12

Miller v. Johnson,

ET eee eae ee 10, 16

Obergefell v. Hodges,

CO Ee TED 7

Pennsylvania Coal Co. v. Mahon,

saan cenaiipbeienbetiosiaeiie 11

Reynolds v. Sims,

I ac sciniceminenaiiionala 8

Shaw v. Reno,

EEE ae aan 6,9

State Farm Mutual Auto. Ins. Co. v. Campbell,

ac ceegetaliineiincoonin 11

Swann v. Charlotte-Mecklenburg Bd. of Educ.,

ES SIS NL eR 10

Texas v. Johnson,

i sallnenaciuaeninlnenel 7

Thornburg v. Gingles,

oh soundonnnnnnbeunnbetued 9, 24

United States v. Lovasco,

ETE RRE RT I Cae nar eee 11

Utah v. Evans,

536 U.S. 452 (2002)............. nein nipiiainnaannaiinysied 6

Vieth v. Jubelirer,

i | SSE eee 5, 20, 21, 25

Wesberry v. Sanders,

Ey EL, 1 TIT... .ccencusccessdduanntounenebeusenuiiieniaaanal 8

White v. Weiser,

' ¢ ¢ 5: EERE ae 8, 23

Whitford v. Gill,

218 F. Supp. 3d 837 (W.D. Wis. 2016)......... 5, 13, 25

Wilson v. Arkansas,

ee Sy Ce I vcinccensiiccstntcepiscnsniadiansnianbeamanaiinel 11

Other Authorities

Michael Altman & Michael P. McDonald, BARD:

Better Automated Redistricting,

42 JOURNAL OF STATISTICAL SOFTWARE 1

TE LEA AS SLE 5 Ea ESR 22

Americans Across Party Lines Oppose Common

Gerrymandering Practices, HARRIS

INTERACTIVE (Nov. 7, 2013),

http://www.theharrispoll.com/politics/America

ns_Across_Party_Lines_Oppose_Common_Ger

rymandering Practices. html ..............0.....00000ceeeeeere 7

John Arbuthnott, An Argument for Divine

Providence, Taken from the Constant

Regularity Observ'd in the Births of Both

Sexes,

27 PHIL. TRANSACTIONS ROYAL Soc’y 186

Ciel iicevesenccuiienbsnssennaniieneionibendmmmtinimiiaaniceasdamiaaaaee 19

Georges Louis Leclerc Buffon, Histoire

Naturelle, Générale et Particuliére (Supp!

ément, Tome Quatriéme (1777))..................0.c0e0seee 22

vil

Jowei Chen & Jonathan Rodden, Cutting

Through the Thicket: Redistricting

Simulations and the Detection of Partisan

Gerrymanders,

14 ELECTION LJ. 331 (2015)...........:.c0ccsccccsereeseeeeee 22

CINDERELLA ACROSS CULTURES (Martine

Hennard Dutheil de la Rochére et al. eds.,

Benjamin Fifield et al., A New Automated

Redistricting Simulator Using Markov Chain

Monetecarlo, available at

http:/Amai.princeton.edu/research/files/redist.

SII ItIEI Thies dnieineidibhiamsabiconedemmosscccsboonsiecceosnccees 22

RONALD A. FISHER, STATISTICAL METHODS FOR

RESEARCH WORKERS (11th ed. 1950)..................... 19

Joshua Fougere, Stephen Ansolabehere &

Nathaniel Persily, Partisanship, Public

Opinion, and Redistricting,

9 ELECTION Lic}. 326 (2010) ...........cecsereccereseeecenneecees 7

Andrew Gelman & Gary King, A Unified Method

of Evaluating Electoral Systems and

Redistricting Plans,

38 AM. J. OF POL. SCIENCE 514 (1994)..............000.. 14

Andrew Gelman & Gary King, Estimating the

Electoral Consequences of Legislative

Redistricting,

85 J. AM. STAT. ASSOC. 274 (1990)........ 12, 18, 20, 24

Andrew Gelman, Gary King, & Andrew Thomas,

Judgelt II: A Program for Evaluating

Electoral Systems and Redistricting Plans

(2010), available at http://j.mp/2ovSNfh. ............... 23

a a aS 15

vill

Heather K. Gerken, Second Order Diversity,

118 HARV. L. REV. 1099 (2005).............00.00-ceceseeseees 16

W.S. GILBERT & ARTHUR SULLIVAN, H.M:S.

ES RT SC A a A 15

Bernard Grofman & Gary King, The Future of

Partisan Symmetry as a Judicial Test for

Partisan Gerrymandering After LULAC v.

Perry,

6 ELECTION Lid. 2 (2007) ........0000:ccccccccccsssoressees 16, 20

Intervening Defendants’ Brief in Response to

the Court’s April 24, 2002 Case Management

Order at 3-5, O’Lear v. Miller, 222 F. Supp. 2d

850 (E.D. Mich. 2002) (No. 2:01-cv-72584-

Gary King & Robert X. Browning, Democratic

Representation and Partisan Bias in

Congressional Elections,

81 AM. POL. Sci. REV. 1251 (1987) ................:000..0005 15

CARL KLARNER ET AL, STATE LEGISLATIVE

ELECTION RETURNS DATA, 1967-2010 (Harvard

Dataverse V1, hdl:1902.1/20401,

UNF:5:q/n5C9RQGfjy6AjbLG6JWQ==, 2013)....... 26

Richard Lowry, CONCEPTS AND APPLICATIONS OF

INFERENTIAL STATISTICS,

http://vassarstats.net/textbook/ch11pt1.htm!....... 19

ESTERS TETAS HELEN SUES PCO Tae ee 15

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) 20.00.0000 .0.ccececeeeeeeee 16, 20

ix

Anthony J. McGann et al., A Discernable and

Manageable Standard for Partisan

Gerrymandering,

14 ELECTION LJ. 295 (2015) ...............-ccceeccsereeeseees 16

John F. Nagle, Measures of Partisan Bias for

Legislating Fair Elections,

14 ELECTION L.J. 346 (2015) ...000000.000000.0cccce cece 16, 20

Karl Pearson, Contributions to the Mathematical

Theory of Evolution, II: Skew Variation in

Homogeneous Material,

PHIL. TRANSACTIONS ROYAL Soc’y (1895).............. 21

Petitioner's Opening Brief, Maestas v. Hall, 274

P.3d 66 (N.M. 2012) (No. 33,387), 2012 WL

SIT iicriticcichiisaseidasabnpiditidndnididinndinlanidadtinessttescssses 17

Plaintiffs’ Initial Closing Brief, Romo v. Detzner,

No. 2012-CA-000412, 2014 WL 3797315 (Fla.

Cir. Ct. July 10, 2014) (Nos. 2012-CA-000412,

2012-CA-00490), 2014 WL 425438739 .............0000..... 17

PRINCETON GERRYMANDERING PROJECT,

ZerryMander. princeton.edy ...........6.....c0ceececeeeeeceeee 23

JOHN RAWLS, A THEORY OF JUSTICE (rev. ed.

AREER Pe DRIER S21 eS ee 15

RICHARD RHODES, THE MAKING OF THE ATOMIC

EEE EERE Ree 22

WILLIAM SHAKESPEARE, A MID-SUMMER NIGHT’S

a nsitedusdbonience 15

WILLIAM SHAKESPEARE, TWELFTH NIGHT.................. 15

Nicholas O. Stephanopoulos & Eric M. McGhee,

Partisan Gerrymandering and the Efficiency

Gap,

82 U. CuI. L. REV. 831 (2015)..................... 12, 16, 20

a

Student, The Probable Error of a Mean,

6 BIOMETRIKA 1 (1908)................ccccecceceseeceeceeees 19, 20

Wendy K. Tam Cho & Yan Y. Liu, Toward a

Talismanic Redistricting Tool: A

Computational Method for Identifying

Extreme Redistricting Plans,

15 ELECTION L.J. 361 (2016) ................ccccccceeececceees 22

MARK TWAIN, THE PRINCE AND THE PAUPER

I esslil 15

G. UDNY YULE & MAURICE G. KENDALL, AN

INTRODUCTION TO THE THEORY OF STATISTICS

LS RS AO 19

Sam Wang, Let Math Save Our Democracy, N.Y.

, ETS eC 27

Samuel S.-H. Wang, Three Practical Tests for

Gerrymandering: Application to Maryland

and Wisconsin,

15 ELECTION L.J. 367 (2016) ...................... 25, 26, 27

Samuel S.-H. Wang, Three Tests for Practical

Evaluation of Partisan Gerrymandering,

68 STAN. L. REV. 1263 (2016) .....................000. passim

INTEREST OF AMICI CURIAE'’

Amici Heather K. Gerken, Jonathan N. Katz,

Gary King, and Samuel S.-H. Wang are experts in the

study of elections.2 They seek to share their

knowledge with the Court about the partisan

symmetry standard.

Amicus Heather K. Gerken is the Dean and the

Sol & Lillian Goldman Professor of Law at Yale Law

School. One of the country’s leading experts in the

fields of election and constitutional law, her scholarly

work includes articles on race, politics, and

redistricting. Her work has been the subject of several

symposia and featured in the Aflantic, the Boston

Globe, and the New York Times, among other journals.

Her 2009 book, The Democracy Index: Why Our

Election System is Failing and How To Fix It, led the

Pew Charitable Trust to create an Election

Performance Index. Dean Gerken is a member of the

American Academy of Arts and Sciences.

Amicus Jonathan N. Katz is the Kay Sugahara

Professor of Social Sciences and Statistics at the

California Institute of Technology. He is an elected

fellow of the American Academy of Arts and Sciences

and the Society for Political Methodology as well as a

former fellow of the Center for Advanced Study in the

' All parties have consented in writing to the filing of this

brief through letters on file with the Clerk. No counsel for a party

authored this brief in whole or in part, and no person other than

amici curiae and their counsel made a monetary contribution

intended to fund the preparation or submission of this brief.

* Title and institutional affiliation are provided for

identification purposes only. The views expressed herein should

not be regarded as those of the institution.

2

Behavioral Sciences. He has written numerous

articles published in leading journals and is currently

the co-editor of Political Analysis, the journal of the

Society for Political Methodology. Professor Katz has

done extensive research on American elections and on

statistical methods for analyzing political science

data. A member of the Caltech/MIT Voting Technology

Project, he has testified or consulted in numerous

elections cases for both Democratic and Republican

clients.

Amicus Gary King is the Albert J. Weatherhead

III University Professor at Harvard University and

Director of the Institute for Quantitative Social

Science. King develops and applies empirical methods

in many areas of social science research, focusing on

innovations that span the range from statistical

theory to practical application. King is an elected

Fellow in eight honorary societies and has won more

than forty "best of" awards for his work. King was

elected President of the Society for Political

Methodology (1997-1999) and Vice President of the

American Political Science Association (2003-2004).

He has been a member of the Senior Editorial Board

at Science (2015-2016), Visiting Fellow at Oxford

(1994), and Senior Science Adviser to the World

Health Organization (1998-2003). His more than 150

journal articles, 20 open source software packages,

and eight books span most aspects of political

methodology, many fields of political science, and

several other scholarly disciplines. Professor King’s

work on legislative redistricting has been used in most

American states by legislators, judges, lawyers,

political parties, private parties, and the United

States Supreme Court.

3

Amicus Larry J. Sabato is the director of the

University of Virginia Center for Politics and the

Robert Kent Gooch Professor of Politics. He is a

leading expert on American politics. His weekly e-

newsletter, "Sabato's Crystal Ball,” is a widely read

publication about elections. Professor Sabato has

written or edited twenty-five books on politics. In his

forty years at the University of Virginia, Sabato has

taught 20,000 students and has received the

University's highest honor, the Thomas Jefferson

Award. He has also won three Emmys for historical

documentaries produced for public television.

Amicus Samuel S.-H. Wang is a professor of

neuroscience and molecular biology at Princeton

University, and facuity associate in the Program in

Law and Public Affairs. He is well known for

developing statistical methods to analyze United

States elections, and he is the author of several works

on statistical methods to detect partisan bias in

redistricting. His election work has won awards from

the Washington Post and Common Cause, and has

been featured in the New York Times, the Wall Street

Journal, the Los Angeles Times, and other

publications. Professor Wang has also received a

National Science Foundation Young Investigator

Award and a McKnight Technological Innovations in

Neuroscience Award for his work investigating the

brain. In 2015, Governor Chris Christie appointed

Professor Wang to the New Jersey Governor's Council

for Medical Research and Treatment of Autism.

4

SUMMARY OF ARGUMENT

Plaintiffs ask this Court to do what it has done

many times before. For generations, it has resolved

cases involving elections and cases on which elections

ride. It has adjudicated controversies that divide the

American people and those, like this one, where

Americans are largely in agreement. In doing so, the

Court has sensibly adhered to its long-standing and

circumspect approach: it has announced a workable

principle, one that lends itself to a manageable test,

while allowing the lower courts to work out the precise

contours of that test with time and experience.

Partisan symmetry, the principle put forward by

the plaintiffs, is just such a workable principle. The

standard is highly intuitive, deeply rooted in history,

and accepted by virtually all social scientists. Tests for

partisan symmetry are reliable, transparent, and easy

to calculate without undue reliance on experts or

unnecessary judicial intrusion on state redistricting

judgments. Under any of these tests, Wisconsin’s

districts cannot withstand constitutional scrutiny.

5

ARGUMENT

The path for resolving this case is clear because

the Court has trod it so many times before. For

generations, the Court has resolved controversies

involving elections and those on which elections ride.

It has decided cases that affect every part of the

democratic process. It has adjudicated questions that

divide us and those where, as here, the American

people are largely in agreement.

In most of these cases, the Court has followed the

same circumspect and sensible route. It has

articulated a constitutional principle and identified a

“workable standard,” Vieth v. Jubelirer, 541 U.S. 267,

311 (2004) (Kennedy, J., concurring in the judgment),

for vindicating that principle while leaving the precise

test to the “crucible of adversarial testing,” Maslenjak

v. United States, 137 S. Ct. 1918, 1931 (2017)

(Gorsuch, J., concurring).

Here, the constitutional principle animating

plaintiffs’ complaint is easy to grasp. In order to

protect its own control of the legislature, one political

party has hijacked the power of the state in order to

“malkje fruitless,” League of United Latin Am.

Citizens (LULAC) v. Perry, 548 U.S. 399, 440 (2006),

another party’s efforts to mobilize and put its

members’ ideas into action. As a result, plaintiffs

allege that Wisconsin’s legislative maps make it

harder for one party to control the state legislature

than the other. Whitford v. Gill, 218 F. Supp. 3d 837,

854-55 (W.D. Wis. 2016).

A workable standard for vindicating this principle

is readily available: partisan symmetry. Partisan

symmetry has its roots in the simplest, most intuitive

6

test for detecting discrimination: what would happen

if the tables were turned? Social scientists have

overwhelmingly endorsed the partisan-symmetry

standard, and for decades courts have deployed

similar tests in other areas of the law.

While this Court need not identify the precise test

for measuring partisan symmetry, the Court must

assure itself that the standard lends itself to a

manageable test. Measures of partisan symmetry

must be transparent, difficult to manipulate,

adaptable to context, and assessed without undue

reliance on experts. Partisan-symmetry tests can

easily meet those conditions.

Under any partisan-symmetry test, Wisconsin’s

legislative districts are grossly asymmetrical.

Measured against other states, Wisconsin’s map is

extreme. As a result, the Court can affirm the decision

of the district court without privileging a specific test.

I. The Court’s Long-Standing Practice Is To

Identify A Workable Principle That Lends

Itself To A Manageable Test While Allowing

The Lower Courts To Refine That Test Over

Time.

The Court has long adjudicated cases involving

elections. It has entertained constitutional claims

governing virtually every aspect of the election

system, including apportionment, Utah v. Evans, 536

U.S. 452 (2002); districting, LULAC v. Perry, 548 U.S.

399 (2006); Shaw v. Reno, 509 U.S. 630 (1993); Baker

v. Carr, 369 U.S. 186 (1962); campaign finance,

Citizens United v. FEC, 558 U.S. 310 (2010);

McConnell v. FEC, 540 U.S. 93 (2003); election

administration, Crawford v. Marion Cty. Election Bd.,

7

553 U.S. 181 (2008); Burdick v. Takushi, 504 U.S. 428

(1992); and party regulation, California Democratic

Party v. Jones, 530 U.S. 567 (2000). Nor has the Court

shirked its constitutional duties in cases that — unlike

this one’ — divide the American people. See, e.z.,

Obergefell v. Hodges, 135 S. Ct. 25%4 (2015); Grutter v.

Bollinger, 539 U.S. 306 (2003); Texas v. Johnson, 491

U.S. 397 (1989); Loving v. Virginia, 388 U.S. 1 (1967);

Brown v. Bd. of Educ., 347 U.S. 483 (1954).

A. The Court Has Repeatedly Followed This

Cautious Practice In Elections Cases.

In most elections cases, the Court has wisely

followed the same cautious course. It has articulated a

workable principle that lends itself to a manageable

test while allowing the lower courts to adapt and

refine that test over time. That same approach has

also informed its work in other areas, including some

of the most contentious cases in constitutional law.

This Court has taken this circumspect approach

repeatedly in the context of districting. In the wake of

its pronouncements in Baker, the Court identified the

* Seventy-one percent of Americans believe that those who

stand to benefit from redistricting should not have a say in how

they are redrawn. Americans Across Party Lines Oppose Common

Gerrymandering Practices, HARRIS INTERACTIVE (Nov. 7, 2013),

http:?//www.theharrispoll.com/politics/Americans_Across_Party_

Lines_Oppose Common_Gerrymandering Practices.html.

People across the political spectrum, including 74% of

Republicans, 73% of Democrats, and 71% of independent voters,

subscribe to this view. Id.; see also Joshua Fougere, Stephen

Ansolabehere & Nathaniel Persily, Partisanship, Public Opinion,

and Redistricting, 9 ELECTION L.J. 325, 325 (2010).

8

core principle undergirding the constitutional claim in

broad, general terms. The Constitution, the Court

wrote in Wesberry v. Sanders, “mak[es] equal

representation for equal numbers of people the

fundamental goal for the House of Representatives.”

376 U.S. 1, 18 (1964). So, too, in Reynolds v. Sims, this

Court held that “[fJull and effective participation by all

citizens in state government requires . . . that each

citizen have an equally effective voice in the election of

members of his state legislature.” 377 U.S. 533, 565

(1964).

In neither of these early cases did the Court

identify the precise test for assessing violations of the

one person, one vote principle. See id. at 569, 579;

Wesberry, 376 U.S. at 18. Instead, it allowed the lower

courts to refine and adapt this principle to fact

patterns raised by subsequent litigation before

settling on an enduring test. As the Court predicted in

Reynolds, “(llower courts can and assuredly will work

out more concrete and specific standards for

evaluating state legislative apportionment schemes in

the context of actual litigation.” 377 U.S. at 578. Its

view that “[djeveloping a body of doctrine on a case-by-

case basis .. . provide(s} the most satisfactory means

of arriving at detailed constitutional requirements,”

id., in redistricting was amply borne out by

subsequent decisions. See, e.g., Karcher v. Daggett, 462

U.S. 725 (1983); White v. Weiser, 412 U.S. 783 (1973);

Mahan v. Howell, 410 U.S. 315 (1973); Wells v.

Rockefeller, 394 U.S. 542 (1969); Kirkpatrick v.

Preisler, 394 U.S. 526 (1969); Avery v. Midland Cty.,

390 U.S. 474 (1968).

The Court has proceeded in a similarly careful

fashion in the context of the Voting Rights Act,

9

crafting doctrines to govern the often-fraught

intersection of politics and race. In Thornburg v.

Gingles, this Court declined to establish a “simple

doctrinal test for the existence of legally significant

racial bloc voting,” 478 U.S. 30, 58 (1986), choosing

instead to offer “general principles [to] provide courts

with substantial guidance in determining” whether

unlawful vote dilution has occurred. Jd. at 58-59. And

in Johnson v. De Grandy, the Court deliberately

developed a “substantial proportionality” standard

without fashioning a mechanistic test. 512 U.S. 997,

1016 (1994); see also id. at 1020-21 (“No single

statistic provides courts with a shortcut to determine

whether a set of single-member districts unlawfully

dilutes minority voting strength.”). Over time, with

the assistance of the lower courts‘ and the benefit of

experience, the Court has refined these tests to protect

equal minority participation without “unnecessarily

infusling] race into virtually every redistricting.”

LULAC, 548 U.S. at 405; see also Bartlett v.

Strickland, 556 U.S. 1, 14 (2009).

The Court’s racial gerrymandering jurisprudence

has followed the same path. In Shaw, the Court

announced that “race-based districting by our state

legislatures demands close judicial scrutiny.” 509 U.S.

at 657. Over time, with the benefit of wisdom gleaned

from experience, the Court delineated the contours of

* See, e.g., League of United Latin Am. Citizens v. Clements,

999 F.2d 831, 857 (5th Cir. 1993) (explaining that Section 2

prohibits racial vote dilution but not partisan political defeat);

Campos v. City of Baytown, 840 F.2d 1240, 1248 (5th Cir. 1988)

(upholding factual determination that Black and Hispanic voters

together constituted a cohesive majority coalition).

10

that principle. It made clear, for example, that a

bizarre shape was not a prerequisite for a

constitutional claim, Miller v. Johnson, 615 U.S. 900,

912-13 (1995), that race could not be used as a proxy

for partisanship, Bush v. Vera, 517 U.S. 952, 968-69

(1996), and that the deliberate packing of minority

voters in a district violates the Constitution,

Covington v. North Carolina, 316 F.R.D. 117, 130

(M.D.N.C. 2016), affd, 137 S. Ct. 2211 (2017) (mem).

B. This Circumspect Approach Is Not

Limited To Elections Cases.

This circumspect approach is hardly limited to

election law. In Brown, the Court's approach was

surgical: it announced a critical principle while

avoiding unnecessary pronouncements that might

have diminished the force of its holding. While a

unanimous Court declared that “separate educational

facilities are inherently unequal,” 347 U.S. at 495, it

left the specifics of antidiscrimination doctrine to

develop over a series of fact patterns and institutional

contexts, see, e.g., Keyes v. Sch. Dist. No. 1, 413 U.S.

189 (1973); Swann v. Charlotte-Mecklenburg Bd. of

Educ., 402 U.S. 1 (1971); Green v. Cty. Sch. Bd., 391

U.S. 430 (1968).

Other areas of constitutional law have similarly

developed after this Court identified a manageable

standard but demurred from announcing a particular

test for assessing it. Wilson v. Arkansas, for example,

declared that circumstances might exist where

unannounced entry would be constitutional, but “le[ft]

to the lower courts the task of determining the

circumstances” when such an entry would survive

scrutiny. 514 U.S. 927, 936 (1995). And United States

ll

v. Lovasco announced the “fundamental conceptions of

justice” standard for assessing the constitutionality of

pre-indictment delays, but gave lower courts the

opportunity to decide what facts met that standard.

431 U.S. 783, 790, 796-97 (1977).

Similar examples abound in such divergent fields

as antidiscrimination law, Harris v. Forklift Systems,

Inc., 510 U.S. 17, 21-22 (1993); antitrust law, FTC v.

Actavis, Inc., 133 8. Ct. 2223, 2238 (2013); takings law,

Pennsylvania Coal Co. v. Mahon, 260 U.S. 393, 416

(1922); patent law, Global-Tech Appliances, Inc. v.

SEB S.A., 563 U.S. 754, 769 (2011); and remedies law,

State Farm Mutual Auto. Ins. Co. v. Campbell, 538

U.S. 408, 425-26 (2003).

It is not surprising that the Court routinely

follows this modest approach in adjudicating

constitutional claims. While the Court is well-

practiced at identifying workable standards, precise

tests for implementing those standards are best

developed over time. This careful approach allows the

Court to take advantage of the experience and

expertise accumulated across cases and contexts.

Rather than trying to judge the merits of a statistical

test entirely on its own, it is able to harness the

energies of the adversarial process and assure itself of

the reliability of the test. As Justice Gorsuch recently

observed:

Respectfully, it seems to me at least

reasonably possible that the crucible of

adversarial testing on which we usually

depend, along with the experience of our

thoughtful colleagues on the district and

circuit benches, could yield insights (or reveal

pitfalls) we cannot muster guided only by our

12

own lights... . Other circuits may improve

that guidance over time too. And eventually

we can bless the best of it.

Maslenjak, 137 S. Ct. at 1931-32 (opinion of Gorsuch,

J.).

C. Now Is The Time For The Court To Act.

Now is the moment for the Court to begin this

important process of testing and reflection. As voters

and legislators have become more loyal to their

parties, partisan self-interest threatens to swamp the

districting process. See Andrew Gelman & Gary King,

Estimating the Electoral Consequences of Legislative

Redistricting, 85 J. AM. STAT. ASSOC. 274, 281 (1990)

(hereinafter Gelman & King); Nicholas 0.

Stephanopoulos & Eric M. McGhee, Partisan

Gerrymandering and the Efficiency Gap, 82 U. CHI. L.

REV. 831, 872 (2015). Gerrymanders are growing in

effectiveness, dramatically amplifying the natural

effects of population clustering. Samuel S.-H. Wang,

Three Tests for Practical Evaluation of Partisan

Gerrymandering, 68 STAN. L. REV. 1263, 1267-68

(2016) (hereinafter Wang, Three Tests).

In addition, new technology makes it increasingly

easy for legislatures to craft partisan gerrymanders

that “separate different populations of voters in

exquisite detail.” Wang, Three Tests, supra, at 1267.

Because “(tlhe first instinct of power is the retention

of power,” McConnell, 540 U.S. at 264 (Scalia, J.,

concurring in part and dissenting in part), these new

tools create the risk that legislative majorities—if left

to their own devices—wil) hold power indefinitely even

if their political support substantially erodes.

13

Litigants and lower courts await the Court’s

guidance on this crucial issue. If the Court remains

quiescent in advance of the 2020 Census, by which

time the tools of redistricters will become even more

effective, the representational harms of which

plaintiffs complain will be inflicted on voters from both

parties in districts across the country.

Il. Partisan Symmetry Is A Workable Standard

With Ancient Roots And Overwhelming

Support From Social Scientists.

A workable standard for adjudicating partisan

gerrymandering claims exists: partisan symmetry.

The standard has already garnered interest from

several Justices. See LULAC, 548 U.S. at 420 (opinion

of Kennedy, J.); id. at 466 (opinion of Stevens, J.); id.

at 483 (opinion of Souter, J.); id. at 492 (opinion of

Breyer, J.). All but universally supported by social

scientists, it is a robust standard that is easy to

understand and to measure. While the absence of

symmetry, standing alone, is not enough to establish

a constitution violation, it should be part of the

broader constitutional inquiry. The district court, for

instance, deployed the symmetry principle as part of a

three-part test to assess whether a map is the product

of discriminatory intent, produces a severe and

durable asymmetry, and lacks a legitimate neutral

justification. Whitford v. Gill, 218 F. Supp. 3d at 884,

903-06.

Partisan symmetry is simple to define: a set of

districts are symmetrical when reversing the outcome

of the election—flipping each party's average district

vote totals—would also reverse the number of seats

won. See, e.g., Wang, Three Tests, supra, at 1281;

14

Andrew Gelman & Gary King, A Unified Method of

Evaluating Electoral Systems and Redistricting Plans,

38 AM. J. OF POL. SCIENCE 514 (1994). The standard

makes no assumptions about the voting behavior of

individual voters but simply assesses how a given plan

translates votes into seats. Symmetry tests do not

mandate proportional representation or require a

particular ratio of seats to votes. They merely measure

whether members of both parties have a chance to

translate votes into seats in the same way.

A. Partisan Symmetry Is A Deeply Intuitive

Standard With Ancient Roots.

Partisan symmetry is a deeply intuitive standard

for measuring discrimination. It asks a simple

question: what would happen if the tables were

turned? This standard does not require the Court to

micromanage legislators or usurp the role of a state’s

legislative branch. It simply requires a legislature to

apply its chosen districting criteria in an evenhanded

fashion. Just as it would be unfair if one candidate had

to win many more votes within a district than his

opponent in order to take office, so, too, it would be

unfair if one party had to win many more votes than

the other in order to win the same number of seats.

Needless to say, much of the statistical work in

discrimination law is designed to answer the same

question. In Title VII cases, for instance, the Court’s

aim is to test whether a black or female candidate was

treated in the same fashion as a similarly situated

white or male candidate. See, e.g., Bazemore v. Friday,

478 U.S. 385, 395-96 (1986) (per curiam). So, too, in

housing discrimination cases, “testers” are used to

determine whether landlords treat some homebuyers

15

differently than others. Havens Realty Corp. v.

Coleman, 455 U.S. 363, 368 (1982).

While modern discrimination law is replete with

examples of symmetry standards, the principle’s roots

are ancient. One finds, for instance, examples in

Judeo-Christian ethics, Genesis 13:8-9; Matthew 7:12.

The notion of turning the tables is so powerful that it

is a canon of literature, WILLIAM SHAKESPEARE, A MID-

SUMMER NIGHTS DREAM; WILLIAM SHAKESPEARE,

TWELFTH NIGHT; MARK TWAIN, THE PRINCE AND THE

PAUPER (1881), music, W.S. GILBERT & ARTHUR

SULLIVAN, H.M.S. PINAFORE (1878), and moral

philosophy, JOHN RAWLS, A THEORY OF JUSTICE 73-78

(rev. ed. 1999). This measure of fairness is deployed

across cultures. See CINDERELLA ACROSS CULTURES

(Martine Hennard Dutheil de la Rochére et al. eds.,

2016); Heather K. Gerken, Second Order Diversity,

118 Harv. L. Rev. 1099, 1146 & n.124 (2005)

(discussing Japanese tradition). Even children rely on

the time-honored strategy of “I cut, you choose.”

B. Social Scientists Resoundingly Support A

Partisan Symmetry Standard.

Partisan symmetry is a principle that enjoys near

universal support among social scientists. Needless to

say, this type of unanimity is rare in academic circles.

Since the measure was articulated in its modern form

in 1987, see generally Gary King & Robert X.

Browning, Democratic Representation and Partisan

Bias in Congressional Elections, 81 AM. POL. SCI. REV.

1251 (1987), no social scientist has challenged its

theoretical legitimacy or analytical force. Indeed, as

Bernard Grofman and Gary King, the two political

scientists who first brought partisan symmetry to the

16

Court’s attention in LULAC, explain, “social scientists

have long recognized partisan symmetry as the

appropriate way to define partisan fairness... and for

many years such a view has been virtually a consensus

position of the scholarly community.” Bernard

Grofman & Gary King, The Future of Partisan

Symmetry as a dudicial Test for Partisan

Gerrymandering After LULAC v. Perry, 6 ELECTION

L.J. 2, 6 (2007).

In the wake of this Court’s discussion of partisan

symmetry in LULAC, social scientists continued to

refine the theoretical and methodological

underpinnings of partisan symmetry. E.g., Wang,

Three Tests, supra; John F. Nagle, Measures of

Partisan Bias for Legislating Fair Elections, 14

ELECTION L.J. 346 (2015); 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); Grofman & King, supra;

Anthony J. McGann et al., A Discernable and

Manageable Standard for Partisan Gerrymandering,

14 ELECTION L.J. 295 (2015); Stephanopoulos &

McGhee, supra. Each of these articles has endorsed

the partisan-symmetry standard. And no scholarly

piece published after LULAC has cast doubt on this

consensus. The standard is routinely used by plaintiffs

and defendants in litigation. Indeed, amici Gary King

and Jonathan N. Katz have deployed the standard

while serving as expert witnesses for both parties. See

Grofman & King, supra, at 15; see also Intervening

Defendants’ Brief in Response to the Court’s April 24,

2002 Case Management Order at 3-5, O’Lear v. Miller,

222 F. Supp. 2d 850 (E.D. Mich. 2002) (No. 2:01-cv-

72584-JAC-PJK); Petitioner’s Opening Brief, Maestas

17

v. Hall, 274 P.3d 66 (N.M. 2012) (No. 33,387), 2012 WL

3236221, at *6, *24; Plaintiffs’ Initial Closing Brief at

22, Romo v. Detzner, No. 2012-CA-000412, 2014 WL

3797315 (Fla. Cir. Ct. July 10, 2014) (Nos. 2012-CA-

000412, 2012-CA-00490), 2014 WL 4254379.

In short, the standard has now been rigorously

vetted and widely applied, and it remains the

touchstone for measuring fairness in redistricting.

Ifl. Partisan Symmetry Lends Itself To A

Manageable Test With Many Doctrinal

Virtues.

As a deeply intuitive and widely accepted measure

of fairness, partisan symmetry b= many virtues.

Nonetheless, the Court should as.*ve itself that a

partisan-symmetry standard lends itself to a

manageable teat. While the Court need not endorse a

particular test in this case, it must be sure that tests

for partisan symmetry are reliable and difficult to

manipulate. Symmetry tests should deploy actual

election outcomes rather than hypothetical maps

created by experts. Courts should be able to adapt the

symmetry standard to different contexts and apply it

without relying unduly on experts or displacing

appropriate democratic judgments. Finally, symmetry

tests should measure electoral opportunity rather

than guarantee proportional victories and map cleanly

onto the constitutional wrongs that animate

redistricting law. Leading partisan-symmetry tests

easily meet those conditions.

18

A. Partisan Symmetry Relies On The Most

Basic Statistical Measures And Is Thus

Transparent And Easy To Calculate

Without Undue Reliance On Experts.

Partisan symmetry is transparent, easy to

calculate, and does not require undue reliance on

experts. Rooted in statistical science, symmetry tests

are designed to figure out whether a given seat

distribution is the product of traditional districting

principles or partisan manipulation. Gelman & King,

supra, at 280-82. It thus identifies genuine partisan

discrimination while avoiding false positives.

Calculating deviations from the standard is simple

and straightforward. It is possible to identify

deviations without the need for complex modeling.

Indeed, most of the tests for measuring partisan

asymmetry are as straightforward as the test this

Court uses to determine violations of the one-person

one-vote standard.

While a variety of methods exist for calculating

deviations from partisan symmetry, at their core

symmetry tests rely on well-known and well-accepted

statistical methods widely used in classrooms and

courts. They answer the key question in

gerrymandering cases: whether each party has the

same opportunity to translate votes into seats.

Once the basic operation is complete, the court is

left with a symmetry score. All that is left to do is to

assess whether the asymmetry is the result of a factor

the Court may consider legitimate—such as

traditional districting principles or political

geography—rather than intentional discrimination.

19

Gauging the extent of partisan asymmetry is just

as straightforward as identifying whether asymmetry

exists in the first place. One need only rely on basic

statistical methods. Statistical significance tests are

almost three centuries old, measured in a fashion that

is indifferent to the underlying cause, and developed

entirely outside the context of redistricting. See John

Arbuthnott, An Argument for Divine Providence,

Taken from the Constant Regularity Observ'd in the

Births of Both Sexes, 27 PHIL. TRANSACTIONS ROYAL

Soc’y 186 (1710). Indeed, the “Student’s t-test” for

comparing two averages, developed nearly a century

ago by a beer brewer for quality control of hops, has

become the most widely used test in all of science. See

Student, The Probable Error of a Mean, 6 BIOMETRIKA

1 (1908); see, e.g., RONALD A. FISHER, STATISTICAL

METHODS FOR RESEARCH WORKERS 17 (11th ed. 1950);

G. UDNY YULE & MAURICE G. KENDALL, AN

INTRODUCTION TO THE THEORY OF STATISTICS 162-63

(3d ed. 1950); Richard Lowry, Chapter 11: t-Test for the

Significance of the Difference Between the Means of

Two Independent Samples, CONCEPTS AND

APPLICATIONS OF INFERENTIAL STATISTICS,

http://vassarstats.net/textbook/ch11pt1.html.

Unsurprisingly, courts have long used such tests in a

variety of legal contexts. See Castaneda v. Partida, 430

U.S. 482, 496 n.17 (1977) (explaining the concept of t-

testing); see also, e.g., Matrixx Initiatives, Inc. v.

Siracusano, 563 U.S. 27, 40-41 (2011) (securities law);

General Elec. Co. v. Joiner, 522 U.S. 136, 145-46 (1997)

(expert testimony); Bazemore, 478 U.S. at 398 (per

curiam) (employment discrimination).

Using these basic parameters, scholars have

developed a range of partisan-symmetry tests that are

20

adaptable to a range of contexts. In a recent Stanford

Law Review essay, for instance, amicus Samuel S.-H.

Wang proposed three tests to evaluate partisan

gerrymanders, all rooted in partisan symmetry. Wang,

Three Tests, supra, at 1269. These tests search for

disparities between the partisan makeup of the state

and the number of seats won, discrepancies in the

winning vote margins of the two parties (i.e., lopsided

wins by one party), and the construction of seats where

a party performs above the state average. Jd. at 1306-

08. Other scholars have developed similar measures.

E.g., Grofman & King, supra; McDonald & Best,

supra; Nagle, supra; Stephanopoulos & McGhee,

supra; Gelman & King, supra.

Many of these tests are as simple as the test this

Court uses to assess one-person one-vote violations.

One of Professor Wang's three symmetry tests

involves comparing only two factors: the share of

Democratic votes in the districts that Democrats win

and the share of Republican votes in the districts that

Republicans win. Wang, Three Tests, supra, at 1306.

Calculating the significance of the difference using

Student’s t-test is hardly more complicated than the

three-part test for one-person, one-vote violations that

this Court described in Vieth, 541 U.S. at 290

(plurality opinion). Indeed, as Professor Wang states,

the test is performed using Student’s t-test and can be

“worked out using a spreadsheet program such as

Microsoft Excel,” with no statistical background

required. Wang, Three Tests, supra, at 1308-09.

Another of Professor Wangs tests detects

gerrymanders by comparing each party’s median vote

share across districts to its mean vote share. Jd. at

1306-07. This "mean-median difference" is well over a

21

century old. See Karl Pearson, Contributions to the

Mathematical Theory of Evolution, II: Skew Variation

in Homogeneous Material, PHIL. TRANSACTIONS ROYAL

Soc’y (1895) at 343-414. It is similarly

straightforward. Just as “judges can multiply and

divide,” Karcher, 462 U.S. at 751 (Stevens, J.,

concurring), they can add and subtract. As a result,

determining partisan asymmetry does not require

undue reliance on statisticians or other experts.

Partisan-symmetry tests thus possess a

significant advantage over standards that the Court

has rejected in the past. Unlike proposals this Court

has previously discarded, partisan-symmetry analysis

does not require the creation of “hypothetical

district[s].” Vieth, 541 U.S. at 349 (Souter, J.,

dissenting).

B. Partisan-Symmetry Tests Differ

Fundamentally From A _ Proportional

Representation Standard.

Partisan symmetry differs fundamentally from a

“proportional representation” standard, which this

Court bas made clear the Constitution does not

require. See LULAC, 548 U.S. at 403. Partisan-

symmetry tests need not demand any equivalence

between the number of votes won and the number of

seats won. See Wang, Three Tests, supra, at 1285-86.

Instead, they merely ask whether each side has

roughly the same opportunity to translate votes into

seats. For instance, a map would be perfectly

symmetrical if a party that wins 60% of the average

district vote receives 80% of the seats, provided that

the opposing party could do the same.

22

C. Partisan Symmetry Tests Can Distinguish

Between Partisan Manipulation And The

Effects Of Traditional Districting

Principles.

Another important feature of partisan symmetry

tests is that they can distinguish the effects of partisan

interference in the districting process from the effects

of traditional districting principles, such as

compactness and contiguity. Wang, Three Tests,

supra, at 1319-20. Simple simulation techniques that

employ real electoral returns can be used to tease out

the effects—if any—of voter clustering and political

geography to any observed asymmetries. See Wang,

Three Tests, supra, at 1289-98; see also Wendy K. Tam

Cho & Yan Y. Liu, Toward a Talismanic Redistricting

Tool: A Computational Method for Identifying Extreme

Redistricting Plans, 15 ELECTION L.J. 351 (2016);

Jowei Chen & Jonathan Rodden, Cutting Through the

Thicket: Redistricting Simulations and the Detection of

Partisan Gerrymanders, 14 ELECTION L.J. 331 (2015);

Michael Altman & Michael P. McDonald, BARD:

Better Automated Redistricting, 42 JOURNAL OF

STATISTICAL SOFTWARE 1 (2011); Benjamin Fifield et

al., A New Automated Redistricting Simulator Using

Markov Chain Monte Carlo, available at

http://imai. princeton.edu/research/files/redist. pdf.

Like the other tests discussed here, mathematical

simulation is hundreds of years old, see Georges Louis

Leclerc Buffon, Histoire Naturelle, Générale et

Particuliére 100-04 (Supplément, Tome Quatriéme

(1777)), and has been used in its modern form at least

since the development of the atomic bomb, see

RICHARD RHODES, THE MAKING OF THE ATOMIC BOMB

522-60 (1986). Conceptually no more complicated than

23

drawing numbers from a hat, these simulations are

easily done on a desktop computer or using publicly

available software tools. See, e.g., PRINCETON

GERRYMANDERING PROJECT,

gerrymander.princeton.edu.

D. Because Symmetry Tests Do Not Rely On

Subjective Judicial Judgments, They

Generate Highly Predictable Measures

That Do Not Displace Appropriate

Districting Criteria.

The simplicity of partisan-symmetry tests leads to

other doctrinal virtues. These tests are difficult to

manipulate because they do not lend themselves to

subjective judgments. Judges, for instance, need not

adjudicate what those in districting circles deride as

“beauty contests” among competing plans. Vera, 517

U.S. at 977.

Because partisan-symmetry tests do not deploy

difficult-to-replicate analyses that depend heavily on

the judgments of experts, they generate stable, highly

predictable measures of fairness that are accessible to

legislators and citizens alike. See Andrew Gelman,

Gary King, & Andrew Thomas, Judgelt II: A Program

for Evaluating Electoral Systems and Redistricting

Plans (2010), available at http://j|.mp/2ovSNfh.

Symmetry tests are easy to assess in advance and

difficult to manipulate during litigation, something

that is especially appropriate in context like this one.

They thus are “judicially discernible and manageable.”

Davis v. Bandemer, 478 U.S. 109, 123 (1986) (plurality

opinion).

Nor do _ partisan-symmetry tests displace

appropriately democratic criteria. See White v. Weiser,

24

412 U.S. 783, 795-96 (1973) (reminding courts

remedying one person, one vote violations to “honor

state policies” and not disregard “important state

interests,” nor “pre-empt the legislative task”). In

resolving cases using the partisan-symmetry

standard, judges need not impose any particular

districting criteria on legislatures. A legislature can

choose which districting criteria it values most—and

how to rank those criteria relative to one another—so

long as it applies them fairly to both sides. All that

courts need ask of legislatures is that they not

discriminate against those who subscribe to a

competing agenda.

E. Symmetry Tests Measure Opportunity,

Not Outcome, And Are Thus Tailored To

The Constitutional Harm At Issue.

Partisan-symmetry tests measure opportunity,

not outcomes. They assess how easy it is for each party

to translate popular support into political power but

do not guarantee success at the polls. See Gelman &

King, supra. Courts will step in only when a districting

plan makes it much more difficult for voters of one

party to enact their ideas than voters of the other

party given the same support among voters—precisely

the sort of discrimination that has concerned the

Court and Congress in the context of race. See LULAC,

548 U.S. at 438-39; Gingles, 478 U.S. at 46.

For these reasons, the symmetry standard is well-

tailored to the constitutional wrongs at issue in this

case. Because partisan symmetry simply requires that

one side not be substantially disadvantaged by district

lines, it accurately measures whether the state has

denied voters the equal protection of the laws. And

25

because it measures the ability of voters to convert

ideas into majorities—and thus to translate speech

into action—it appropriately reflects the First

Amendment considerations on which the opinion

below rested. Whitford v. Gill, 218 F. Supp. 3d at 880-

84; see Vieth, 541 U.S. at 314-15 (Kennedy, J.,

concurring in the judgment).

F. Partisan Symmetry Tests Are Flexible

And Can Be Deployed Simultaneously To

Ensure That Judges Can Identify Extreme

Outliers And Be Confident In The

Robustness Of Their Findings.

Partisan-symmetry tests offer a final, distinctive

advantage. Partisan-symmetry tests all answer the

same, simple question and rely on a shared standard.

But they are flexible enough to accommodate

contextual differences, thus allowing courts to choose

the test best suited for assessing a particular plan. See,

e.g., Wang, Three Tests, supra, at 1306-09; see also

Samuel S.-H. Wang, Three Practical Tests for

Gerrymandering: Application to Maryland and

Wisconsin, 15 ELECTION L.J. 367, 377-81 (2016)

(hereinafter Wang, Application).

More importantly, a court can assess a districting

plan using more than one symmetry test. Extreme

gerrymanders will certainly perform poorly along

more than one symmetry measure. Judges can thereby

use multiple symmetry tests to assure themselves of

the robustness of their assessment and identify

extreme outliers.

26

IV. Wisconsin’s Legislative Districts Would Fail

Under Virtually Any Partisan-Symmetry

Test The Court Might Choose.

In this case, for instance, Wisconsin’s plan

performs poorly under virtually any measure of

partisan symmetry. After the 2010 redistricting,

Democratic wins have been more lopsided compared

with Republican wins. In the 2010 elections,

legislators in the two parties won approximately

equal-sized victories on average: 65% of the two-party

vote for Democratic legislators and 66% for Republican

legislators.° But in 2012, immediately after

redistricting, the average Democratic win jumped to

69%, while the average Republican win fell to 60%.

The difference, nine percentage points, is highly

unlikely to have arisen in the absence of intentional

discrimination. Indeed, the probability that this

disparity was an unintentional product of a neutral

districting process is less than one in ten million. And

vote-share difference persisted into subsequent

elections. See, e.g., Wang, Application, supra, at 380.

Again, as a statistical matter, it is highly unlikely that

this disparity, which has persisted across three

election cycles, was the product of traditional

districting principles.

A second test, the mean-median difference, is well

suited to closely divided states such as Wisconsin. The

mean-median difference is easy to calculate, and can

®* These numbers were calculated using standard

imputations from the “State Legislative Election Returns” data

set. CARL KLARNER ET AL, STATE LEGISLATIVE ELECTION RETURNS

DaTA, 1967-2010 (Harvard Dataverse V1, hdl:1902.1/20401,

UNF:5:q/n5CORQGfiy6AjbLG6JIWQ==, 2013).

27

be figured with a pencil and paper or a hand

calculator. It derives from the mean and the median,

two statistical quantities that are usually taught to

schoolchildren by the sixth grade. See Sam Wang, Let

Math Save Our Democracy, N.Y. TIMES, Dec. 5, 2015.

After redistricting, in 2012 the average

Democratic vote share across all districts was 51.5%

and the median vote share was 45.7%. That result

would have occurred unintentionally in less than one

out of 100,000 cases. Wang, Application, supra, at 380.

Again, this disparity persisted across three election

cycles. Id.

Just as these results are highly unlikely to have

arisen unintentionally, they cannot be explained by

voters’ geographical sorting or other nonpartisan

mechanisms. Although Appellants claim that “the

facts of political geography” complicate partisan-

symmetry analysis, J.S. 34, partisan-symmetry tests

can take those facts into account.

Such an exercise would not be necessary in

Wisconsin, where partisan asymmetry effectively

arose overnight, immediately after redistricting.

Needless to say, the political geography of Wisconsin

did not change radically during this short period.

In this case, all partisan-symmetry tests point to

the same conclusion: in Wisconsin, partisans

deliberately crafted legislative districts to insulate

themselves from defeat. Those districts ensured one

party could put its ideas into action while denying its

opponents a fair opportunity to translate votes into a

legislative majority. For these reasons, the Court

should adopt a partisan-symmetry standard to

adjudicate partisan gerrymandering claims and strike

28

down Wisconsin’s egregiously gerrymandered

Assembly maps.

CONCLUSION

The judgment of the district court should be

affirmed.

Respectfully submitted,

Kevin K. Russe!! Heather K. Gerken

GOLDSTEIN & Counsel of Record

PC 127 Wall Street

RUSSELL, P. * New CT 06511

7475 Wisconsin Ave. (203) 432-1

Suite 850 heather.k.gerken@

Washington, DC 20814 yale.edu