“The object of districting is to establish ‘fair and effective representation for all citizens.’”124 Partisan bias clearly offers a suitable metric to measure, in at least a preliminary fashion, the “burden a gerrymander imposes on representational rights”125 because it is so clearly rooted in commonsense notions of fairness and equality of treatment,126 and because it is directly linked to the measurement of the effects of partisan gerrymandering. It is also a concept that can be clearly measured and about which evidence can be provided by competent social science testimony.127 Now that members of the Supreme Court have singled out the deviation from partisan symmetry as a potential key indicator of partisan gerrymandering (with partisan bias arguably playing a role analogous to the total population deviation in the one person, one vote cases), we anticipate that there will be new partisan gerrymandering challenges brought. But since the bar has clearly been set high, with the Court’s refusal to invalidate the Texas congressional plan as an unconstitutional partisan gerrymander, we would not anticipate that there will be many such new challenges. What we would expect, though, is that most new challenges will seek to attract the votes of Justice Kennedy, as a pivotal member of the Court, by basing their legal challenges to plans on results of elections already conducted under that plan rather than on prospective assessments of expected severe long term partisan bias. Either way, redistricters, and lawyers arguing redistricting cases, would now be well advised to use the best social science methodologies to estimate the degree to which their plan deviates from partisan symmetry.
As we have emphasized throughout this article, the decision to make use of partisan bias as a prima facie measure of deviation from fairness and equality of treatment leaves open many important legal questions. First, courts will need to consider whether the only relevant evidence of partisan gerrymandering comes from elections actually held under a plan or whether prospective evaluations based on past elections in the same geographic areas might also be probative. This is a topic about which we briefly commented in Section II of our article. Second, courts will need to address the question of what is an appropriate legal threshold for a level of partisan bias that would trigger a prima facie claim of violation of equal protection. This is a question for which we identified various possible answers in Section III. Third, courts will need to address how other criteria might enter as relevant at some phase of the trial process. This is a topic on which we commented in Section IV.
Now that the Supreme Court has provided the first real guidance to lower courts about how to think about partisan gerrymandering claims based on Bandemer v. Davis, we anticipate that the case law in the area of partisan gerrymandering will evolve much as it has in other areas of voting rights – namely deliberately but steadily, and with only occasional further intervention by the Supreme Court to clarify inconsistencies that arise among lower court judgments.128 The plurality opinion in Vieth quotes from an earlier statement by Bernard Grofman: ("[A]s far as I am aware I am one of only two people who believe that Bandemer makes sense. Moreover, the other person, Daniel Lowenstein, has a diametrically opposed view as to what the plurality opinion means").129 We find nothing to argue with in that statement, but take from it a very different implication than that drawn by the plurality in Vieth. We believe that perhaps the single most important reason that lower courts have not developed a manageable standard for judicial review of partisan gerrymandering claims in the two decades since Bandemer is that Bandemer and subsequent Supreme Court decisions about partisan gerrymandering failed to provide lower courts adequate guidance about the directions along which such standards might develop.130 In our view, if we look closely at the various opinions in LULAC, we can see that the Supreme Court has seeded the clouds after this 20 year drought.131We think that, at last, there can now be a non-trivial probability of rain,and as a result to a new flowering of American democracy less affected by the ills of partisan gerrymandering. It will now be up to lower courts in future cases to make concrete the ideas about tests for partisan gerrymandering found in LULAC.
* Bernard Grofman (http://www.socsci.uci.edu/~bgrofman/) is Professor of Political Science at the University of California, Irvine. The Supreme Court, as well as many lower federal courts, have cited his research on racial voting patterns and other topics related to elections on numerous occasions, perhaps most notably in Thornburg v. Gingles, 478 U.S. 30, 52-53 & n. 20 (1986), one of the roughly twenty voting rights cases in nearly a dozen states where he has served as an expert witness. Grofman has also twice been a consultant to the Special Master in the Federal District Court, Southern District of New York, in cases where the failure of the legislator and governor to reach agreement forced the court to propose a congressional redistricting plan of its own for the State of New York.
Gary King (http://GKing.Harvard.edu) is David Florence Professor of Government, and Director of the Institute for Quantitative Social Science, at Harvard University. The methods he and his coauthors developed are widely used by courts and experts in redistricting litigation. So that he and others could implement these methods, he wrote and freely distributes the software programs JudgeIt (along with Andrew Gelman), for measuring partisan bias and electoral responsiveness in districting plans, and EI, for measuring racially polarized voting from available electoral and census data. Both are widely used in academia, redistricting processes, and redistricting litigation. He has served as an expert witness or consultant in about a third of the U.S. states during their redistricting processes. He can be reached at 1737 Cambridge Street, Harvard University, Cambridge MA 02138; King@Harvard.Edu, 617-495-2027.
We are indebted to Justin Nelson for assistance with an Amicus Brief on Behalf of Neither Party which we submitted (along with Andrew Gelman and Jonathan Katz) to the U.S. Supreme Court in Jackson v. Perry, to Clover Behrend-Gethard for secretarial assistance in preparing this paper, and to the Library of Congress (PA#NDP03-1), the National Science Foundation (SES-0318275, IIS-9874747), and the National Institutes of Aging (P01 AG17625-01) for research support. We are also indebted to Marshall Hurley Esq. for having provided us updated information on the rules for election of Superior Court judges in North Carolina.
1 Davis v. Bandemer 478 U.S. 109 (1986)
2 Vieth v. Jubilerer 541 U.S. 267 (2004)
3 LULAC v. Perry 126 S. Ct. 2594 (2006), This case consolidated Nos. 05-204, 05-254, 05-276, and 05-439. It was decided on June 28, 2006.
4 The plan used for the 2002 congressional elections in Texas was a court-drawn plan whose constitutionality was upheld by the Supreme Court in Balderas v. Texas, 536 U.S. 919 (2002). When the 2002 elections resulted in a shift of the state into Republican control of both branches of the state legislature as well as control of the governorship, after much travail involving Democratic legislators who fled the state to break legislative quorum requirements, the Republican-controlled legislature passed a plan in 2003 which resulted in six additional Republican members of congress being elected in 2004. The near farcical elements of the initial Democratic attempts to prevent the Texas legislature from voting on that new congressional districting plan led one political satirist to characterize the situation after the 2004 congressional elections in Texas as: “For the Democrats, reredistricting temporarily delayed became reredistricting DeLayed, but never denied.” (A Wuffle, personal communication, April 1, 2005). In Session v. Perry, 298 F. Supp. 2d 451 (E.D. Tex.) (three-judge court) (per curiam), summarily vacated sub nom. Jackson v. Perry, 543 U.S. 941 (2004), the District Court for the Eastern District of Texas, after hearing argument on this issue, said the 2003 Texas plan was not an unconstitutional gerrymander. (The District Court also rejected the claim that the plan violated Section 2 of the Voting Rights Act.) That decision was vacated and remanded to the District court in the light of Vieth, 541 U.S. 941 (2004). After a reexamination of the political gerrymandering claims the District Court again held for the defendants in Henderson v. Perry, 399 F. Supp. 756 (2005), and that decision was appealed to the Supreme Court, on a variety of grounds, under the name LULAC v. Perry.
5 “The sole-intent standard … is no more compelling when it is linked to the circumstances that Plan 1374C is mid-decennial legislation.” LULAC, 126 S. Ct. at 2602 (opn. of Kennedy A.)
6LULAC, 126 S. Ct. at 2652 (opn. of Roberts, C. J.)
7 LULAC, 126 S. Ct. at 2647 (opn. of Souter, D.)
8 Amicus Brief in Jackson v. Perry Submitted on Behalf of Neither Party by Gary King, Bernard Grofman, Andrew Gelman, and Jonathan Katz in the U.S. Supreme Court (No. 05-276), henceforth King et al. (2005). See http://gking.harvard.edu/projects/red.shtml.
9 Although there was majority agreement on each of the issues raised in the case, those majorities were not always made up of the same set of Justices, and the case had six separate opinions.
10 LULAC, 126 S. Ct. at 2638 (n.9) (opn. of Stevens, J. P., joined by Breyer, S).
11 LULAC, 126 S.Ct. at 2641 (opn. of Stevens, J. P.)
12 “Plan 1374C [the challenged plan] is inconsistent with the symmetry standard… .” (LULAC 126 S. Ct. at 2637 (n. 8) (opn. of Stevens, J. P.).
13 LULAC 126 S. Ct. at (opn. of Justice Stevens at ??, with internal quotes citing to ante (opinion of Kennedy, J).
14 LULAC 126 S. Ct. at 2647 (opn. of Souter D.).
15 LULAC 126 S. Ct. at 2647 (opn. of Souter, D. ) with internal quotes citing to the opinion of Kennedy, J. and to the opinion of Stevens, J.
16 LULAC 126 S. Ct. at 2611 (opn. of Kennedy, A. joined by Justices Souter and Ginsburg), emphasis added.
17 LULAC 126 S. Ct. at 2638 (n.9) (opn.of Stevens, with internal cite to opinion of Kennedy, J. ). See also Richard Briffault. 2006. “LULAC on Partisan Gerrymandering: Some Clarity, More Uncertainty, 105 Mich. L. Rev. First Impressions. 58 at 61.
18LULAC 126 S. Ct. at 2651 (Opn. of Chief Justice Roberts, with internal cite quoting from the opinion by Kennedy, J. ante, at 2612.)
19 Only Justice Scalia, joined by Justice Thomas, would vote to reverse Bandemer. These Justices reiterate their view in Vieth that, since “no party or judge has put forth a judicially manageable standard … we should simply dismiss appellants’ claims as nonjusticiable” (LULAC 126 S. Ct. at 2663) (opn. of Scalia A).
20 The consequences of partisan gerrymandering are arguably exacerbated in situations of razor thin legislative majorities and high ideological polarization. (See B. Grofman and G. Jacobson Amicus Brief in Richard Vieth, et al., v. Robert c. Jubelirer, et al. 541 U.S. 267 (2004), S. Hirsch, 2003. “The United States House of Unrepresentative: What Went Wrong in the Latest Round of Congressional Redistricting.” Election Law Journal 2(2): 179-216.
21 LULAC 126 S. Ct. at 2647 (opn. of Souter, D.) We also note that, in Justice Stevens view, “Part III of the Court’s opinion and … my own opinion demonstrate [that] assessing whether a redistricting map has a discriminatory impact on the opportunities for voters and candidates of a particular party to influence the political process is a manageable judicial task” (LULAC 126 S. Ct. at 2636 (n. 5) (opn. of Stevens J.P.)
22 LULAC 126 S. Ct. at 2611(opn.of Kennedy, A.)
23 In Justice Kennedy’s view: “A test that treats these similarly effective power plays in such different ways does not have the reliability that appellants ascribe to it” (LULAC 126 S. Ct. at 2610 (opn. of Kennedy A.
24 However, while this essay is directly relevant to the empirical questions posed by this case related to partisan gerrymandering -- in particular to the conceptualization and measurement of partisan bias -- since we have not fully reviewed the evidentiary record nor conducted independent empirical investigations of our own, we expressed in our Brief and express here no views about the level of partisan bias in the redistricting plan that was at issue nor that in previous plans, nor do we express an opinion as to which party ought to have prevailed in LULAC with respect to the issue of unconstitutional partisan gerrymandering.
25 LULAC 126 S. Ct. at 2638 (n. 9) (opn. Kennedy, A.)
26 Such a standard can satisfy the desire of the plurality in Davis v. Bandemer, 478 U.S. 109 (1986), for “a showing of more than a de minimis effect” (at 134) such that “an actual or projected history of disproportionate results exists, and that the electoral system is arranged in a manner that will consistently degrade a voter’s or a group of voters' influence on the political process as a whole.” (at 132). In the language of Justice Kennedy in LULAC, it must “show a burden, as measured by a reliable standard, on the complainants’ representational rights” (at 2602) (opn.of Kennedy A.)
27 2005, 4-5; op cit.; quoted in LULAC 126 S. Ct. at 2637 (opn. of Stevens, J. P.)
28Although the literature on the fair translation of seats into votes can be traced back more than a century, the most prominent early studies in the modern literature include Edward R. Tufte, The Relationship Between Seats and Votes in Two-Party Systems. 67 American Political Science Review 540-554 (1973) and Bernard Grofman, Measures of Bias and Proportionality in Seats-Votes Relationships, 9 Political Methodology 295- 327 (1983).
29 81 Am. Pol.Sci. Rev. 1251 (1987)
30 Justice Stevens then cites (at pp. 21-22) to a number of the references given in King et al. (2005) in support of this proposition, including Edward R. Tufte, The Relationship Between Seats and Votes in Two-Party Systems. 67 American Political Science Review 540-554 (1973); Gary King and Robert X. Browning in Democratic Representation and Partisan Bias in Congressional Elections, 81 Am. Pol.Sci. Rev. 1251 (1987); Andrew Gelman & Gary King, A Unified Method of Evaluating Electoral Systems and Redistricting Plans, 38 Am. J. Pol. Sci. 514 (1994); Dennis Thompson, Election Time: Normative Implications of Temporal Properties of the Electoral Process in the United States, 98, Am. Pol. Sci. Rev. 51 (2004); and Erik J. Engstrom & Samuel Kernell, Manufactured Responsiveness: The Impact of State Electoral Laws on Unified Party Control of the Presidency and House of Representatives, 1840-1940, 49 Am. J. Pol. Sci. 531 (2005). As explained elsewhere, “[s]cholars have reached near consensus on partisan symmetry as a standard of partisan fairness and have made great progress on developing measures that can be used to see whether electoral systems and districting plans meet this standard.” Gary King, John Bruce & Andrew Gelman, Racial Fairness in Legislative Redistricting, in Classifying by Race 85, 85 (Paul E. Peterson, ed., 1996). There are many other references we could give (see e.g., Ernesto Calvo & Maria Victoria Murillo, Who Delivers? Partisan Clients in the Argentine Electoral Market, 48 Am. J. Pol. Sci. 742 , 2004; and Thomas W. Gilligan & John G. Matsusaka, Structural Constraints On Partisan Bias Under The Efficient Gerrymander, 100 Pub. Choice 65, 1999) to further support this claim. The only alternative standard of fairness that exists in the political science literature is proportionality of seats and votes, but it is widely recognized that a proportionality standard is simply not appropriate for use as a legal standard in plurality based elections, since plurality elections cannot be expected to yield proportional results.
31 LULAC 126 S. Ct. at 2637 (opn. Stevens J. P.), citing to App. 34-42 (report of Professor John R. Alford, expert for Appellants) and id. At 189-193, 216 (report of Professor Ronald Keith Gaddie, expert for the State). Here we would call special attention toGraph 2 in the Alford report, and Fig. 1 in the Gaddie Report.
32 See e.g., Page v. Bartels, 144 F. Supp. 2d 346 (D.N.J. 2000). However, many uses of seats-votes curves by courts and redistricting commissions do not take advantage of the most recent methodological improvements in evaluating partisan symmetry found in the political science literature. (See below.)
33 See,e.g., Gary King, Electoral Responsiveness and Partisan Bias in Multiparty Democracies, 15 Legislative Studies Quarterly, 159, 163-65, 181 (1990).
34For example, partisan symmetry, and associated measures, have been applied to the Electoral College (Gelman, Andrew; Jonathan Katz; and Gary King. "Empirically Evaluating the Electoral College," Chapter 5, pp. 75-88, in Ann N. Criegler, Marion R. Just, and Edward J. McCaffery, eds., Rethinking the Vote: The Politics and Prospects of American Electoral Reform, New York: Oxford University Press, 2004, http://gking.harvard.edu/files/abs/rethink-abs.shtml); Grofman, Bernard, Thomas Brunell, Janet Campagna. 1997. Distinguishing Between the Effects of Swing Ratio and Bias on Outcomes in the U.S. Electoral College, 1900-1992. Electoral Studies, 16(4):471-487; and to delegate selection in presidential election nomination contests (Stephen Ansolabehere and Gary King. "Measuring the Consequences of Delegate Selection Rules in Presidential Nominations," Journal of Politics, Vol. 52, No. 2 (May, 1990): 609-621, http://gking.harvard.edu/files/abs/pri-abs.shtml).
35For a more general discussion of the various types of electoral laws see Introduction, Bernard Grofman and Arend Lijphart (eds.). Electoral Laws and Their Political Consequences. New York: Agathon Press, 1986, esp. pp. 1-3.
36 Davis v. Bandemer, 478 U.S. at 162 (Powell, J., concurring in part and dissenting in part).
37Electoral systems that mandate versions of proportional representation do not necessarily produce partisan symmetry. For example, many European nations that use proportional representation have electoral rules that, as applied, generate electoral systems with sometimes considerable partisan bias. This may occur in a multi-party system when very small parties fall below legal thresholds and so get no seats and as a result larger parties gain more than a proportional share of seats.
38 An exception is Thomas L. Brunell, Rethinking Redistricting: How Drawing Uncompetitive Districts Eliminates Gerrymanders, Enhances Representation, and Improves Attitudes Toward Congress. PS: Political Science & Politics 39 (1): 77-85 (January, 2006).
39Andrew Gelman and Gary King, Estimating the Electoral Consequences of Legislative Redistricting, Journal of the American Statistical Association, 85, 410 (June 1990) at 276.
40 See M.G. Kendall and A. Stuart. The Law of Cubic Proportions in Electoral Results. British Journal of Sociology, 1, 193-196; James G. March Party Legislative Representation as a Function of Election Results, Public Opinion Quarterly, 21, 4, (Winter 1957-58) at 512-542; Phillip A Schrodt, A Statistical Study of the Cube Law in Five Electoral Systems, Political Methodology, 7, 31-53; Bernard Grofman, Measures of Bias and Proportionality in Seats-Votes Relationships, 9 Political Methodology. 295, 327 (1983); Niemi, Richard G. and Patrick Fett. 1986. "The Swing Ratio: An Explanation and an Assessment," Legislative Studies Quarterly, XI,1 (February): 7590; Gary King and Robert X. Browning in Democratic Representation and Partisan Bias in Congressional Elections, 81 Am. Pol. Sci. Rev. 1251 (1987).
41 David E. Butler, Appendix, The British General Election of 1950, H. G. Nicholas, Ed., London: Macmillan, Pp. 305-333.
42See Gary King; Ori Rosen; Martin Tanner; and Alexander F. Wagner. Ordinary Voting Behavior in the Extraordinary Election of Adolf Hitler, (http://gking.harvard.edu/files/abs/naziV-abs.shtml), which offers examples of uniform partisan swing in the U.S. Congress, the Oklahoma State House, the Weimar Republic, and the Parliament of the Russian Federation.
43 See C. Backstrom, L. Robins, and S. Eller. 1978. Issues in Gerrymandering: An Exploratory Measure of Partisan Gerrymandering Applied to Minnesota, Minnesota Law Review, 62 at 1121-1159.
44This approach was built over four successive articles, each which improved on the previous: Gary King. Representation Through Legislative Redistricting: A Stochastic Model, American Journal of Political Science, 33, No. 4 (November, 1989): pp. 787-824; Andrew Gelman and Gary King. Estimating the Electoral Consequences of Legislative Redistricting, Journal of the American Statistical Association, 85,410 (June, 1990): Pp. 274-282; Gary King and Andrew Gelman. Systemic Consequences of Incumbency Advantage in U.S. House Elections, American Journal of Political Science, 35, 1; and Andrew Gelman and Gary King. A Unified Method of Evaluating Electoral Systems and Redistricting Plans, American Journal of Political Science, 38, 2 (May, 1994): Pp. 514-554. The method in the latter article is implemented in the open source and free software called “JudgeIt: A Program for Evaluating Electoral Systems and Redistricting Plans,” by Andrew Gelman and Gary King, http://gking.harvard.edu/stats.shtml#judgeit.
45 A partial exception is when we have a massive realignment under way, but in many such situations, it is usually the case that, within any given state, electoral tides are moving generally in the same direction and so the assumption still holds.
46 In any challenge to a plan as an unconstitutional partisan gerrymander courts will apply the traditional criteria for admitting expert evidence and determine in each case (1) whether the experts are qualified; and (2) whether their particular analyses are reliable. Indeed, as noted earlier, courts regularly use statistics in a number of different areas of voting rights law. For example, statistical measures are commonly used to determine levels of racial bloc voting and to help decide whether a minority group can elect a candidate of its choice (see Thornburg v. Gingles, 478 U.S. 30, 52-53 (1986)). In each instance, the court must make a judgment about the expert and the methodology. For a thorough discussion of the different statistical standards used to determine whether a plaintiff has met the Gingles test and their reliability, see Bone Shirt v. Hazeltine, 336 F. Supp. 2d 976, 995-1005 (D.S.D. 2004) (discussing the various standards and surveying cases that apply these standards).
47 Davis v. Bandemer, 478 U.S. 109 (1986).
48 Indeed, failure to take into account anticipatable changes over time in voter support (i.e., failing to read the “handwriting on the wall”) can convert a plan that was intended to have been gerrymandered to favor Party A into a plan whose actual consequences are to favor party B. See Grofman, Bernard and Tom Brunell. 2005. The Art of the Dummymander: The Impact of Recent Redistrictings on the Partisan Makeup of Southern House Seats. In Galderisi, Peter (Ed.) Redistricting in the New Millennium. Lexington Press, pp. 183-199.
49 For a discussion of efficient partisan gerrymandering see Owen, Guillermo and Bernard N. Grofman. 1988. Optimal partisan gerrymandering. Political Geography Quarterly, 7(1):5 22.
50 The minority party members are given really safe seats with the intention of concentrating the votes of their party’s supporters in as few seats as possible; but the members of the majority party are also given safe seats, now with the intention of making sure that those seats remain safe over the course of subsequent elections
51 As noted in the plurality opinion in Vieth at 571-2, “efforts to maximize partisan representation statewide might well begin with packing voters of the opposing party into the districts of existing incumbents of that party. By this means an incumbent is protected, a potential adversary to the districting mollified, and votes of the opposing party are diluted.”
52 LULAC 126 S. Ct. at 2611 (opn. of Kennedy, A.) Justice Breyer in Vieth refers to situations where a majority party in votes has twice been denied a majority of seats as evidence which might compensate for the absence of other indicia of unjustified entrenchment of a minority party in power.
53 Davis v. Bandemer 478 U.S. 109, 140 (1986)
54 Vieth, 541 U.S. at 312 (Kennedy, J., concurring in the judgment).
55 A variant of this point is made by Justice Souter (joined by Justice Ginsburg) in their dissenting opinion in Vieth, at 602 who argue that, to bring a successful partisan gerrymandering claim, it must be shown that plaintiffs are a member of a politically “cohesive” group. However, we would emphasize that the test we propose, based on behavior at the level of units of geography, is less restrictive than that suggested by Justices Souter and Ginsburg, since our test refers only to the potential for partisan gerrymandering based on geographically-based districts, and does not require analysis at the individual voter level..
56 See Bernard Grofman, Declarations in Badham v. Eu (excerpts). PS (Summer 1985): 544 549, 573 574; cf. Bernard Grofman. Introduction to Minisymposium on Political gerrymandering: Badham v. Eu, Political science Goes to Court. PS (Summer 1985.): 538 543.
57 These predictions were reported in Andrew Gelman and Gary King. A Unified Method of Evaluating Electoral Systems and Redistricting Plans," American Journal of Political Science, Vol. 38, No. 2 (May, 1994): Pp. 514-554.
58 LULAC 126 S. Ct. at 2626-2637 (n. 6) App. To Juris Statement at 225a (declaration of John R. Alford, Ph.D.). Justice Stevens (n. 7 at p. 20) notes that Republicans won “21 of the 22 seats that had been designed to favor Republicans in Plan 1374C,” and goes on to comment that the evidence suggests that the lone exception, Representative Edwards, who won by only 51% of the vote, may not be safe in 2006.
59 LULAC 126 S. Ct. at 2640 (opn. of Stevens, J. P.)
60 At pp. 18-19,n.10.
61 See e.g., State Appellees Brief in Jackson v. Perry, at p. 46.
62 In the plurality opinion in Vieth authored by Justice Scalia, the Court reiterates its long standing view that “the Constitution provides no right to proportional representation.” This is a legal conclusion, and so not in our purview, but in any case, not one with which we would disagree. Indeed, we would note that the use of plurality elections in single seat and multi-seat districts (and in at-large elections) at the time of the founding reinforces the view that the Constitution has no mandate for proportional representation in either method or result, and the continued use of plurality-based elections after the passage of the Civil War Amendments further reinforces this conclusion. However, the plurality opinion in Vieth, also asserts that the claim that a map is unconstitutional because it “can thwart the plaintiffs’ ability to translate a majority of votes into a majority of seats” is equivalent to requiring proportional representation. That is a statement about political science methodology, and one that is erroneous. Nonetheless, we should also be equally clear that in this Article we are not asserting that any plan that thwarts a party’s ability to translate a majority of votes into a majority of seats must necessarily be held unconstitutional. Rather, we are simply proposing a way to measure the magnitude of partisan bias, and leaving it entirely up to the Supreme Court to determine the magnitude of (durable) partisan bias that rises to the level of a (prima facie) constitutional violation. See extended discussion of the issue of thresholds and manageable standards in Section 4.
63 Brief of Appellees Tina Benkiser, Chairman, Republican Party of Texas, and John DeNoyelles in Jackson v. Perry, at pp. 21-26).
64 Vieth 541 U.S. 267 at 552.
65 Vieth 541 U.S. 267 at 286 (internal citations omitted).
66 Vieth 541 U.S. 267 at 287.
67 Put differently, a partisan symmetry test for the magnitude of partisan bias is easy to apply in normal, healthy, democratic electoral systems. That is because in such systems, not everyone always votes consistently for the same party.
68 Similarly, as we discuss in Section 5, applying the symmetry methodology to evaluate the equality of treatment for groups with fixed characteristics, such as race, is not sensible.
69 The problem of counterfactuals (or hypotheticals) posed so far from the data that measurement is difficult or impossible is an important general issue in statistical analysis. See for example Gary King and Langche Zeng. The Dangers of Extreme Counterfactuals, Political Analysis, Vol. 14, No. 2, 2006; Gary King and Langche Zeng. When Can History be Our Guide? The Pitfalls of Counterfactual Inference, International Studies Quarterly, 2006, forthcoming.
70 Applying the symmetry standard to a political system with consistent one-party control is not feasible or relevant. In electoral systems that do not function as democracies, or have some non- or semi-democratic features such as de jure or de facto one-party rule, or the total absence of partisan competition, other features of the electoral system would need to be studied (or remedied) before it would be reasonable to assess the degree and direction of partisan bias.
71 However, one qualification is necessary. For state redistricting of Congressional elections, since Congress could be nationally competitive while locally uncompetitive, or nationally uncompetitive while locally competitive, in these situations, we would propose to apply the methodology where either consideration was applicable. However, we recognize that the choice as to how to delimit the domain of cases to which the partisan bias methodology would be applied is ultimately a legal issue even though some restrictions (e.g., to settings that are potentially competitive) are necessary for purely statistical reasons.
72 In Jackson v. Perry at p. 47
73 In the Brief of Appellees Tina Benkiser, Chairman, Republican Party of Texas, and John DeNoyelles where they claim (at p. 18)
74 As suggested earlier, courts often rely on expert witness testimony to do just that. For example, in Balderas v. Texas, 536 U.S. 919 (2002), the District court used the number of districts leaning in favor of each party based on prior election results to estimate which congressional districts could be expected to lean toward each party.
75 Justice Souter’s opinion in Vieth, 158 L. Ed. 2d 546, at 602 cites to various sources supporting the view that partisan gerrymandering has been made easier given modern computer technology (e.g., R. Pildes, Principled Limitations on Racial and Partisan Restricting, 106 Yale L. J. 2505, 2553-2554 (1997) ("Recent cases now document in [microscopic] detail the astonishing precision with which redistricters can carve up individual precincts and distribute them between districts with confidence concerning the racial and partisan consequences"); and Morrill, A Geographer's Perspective, in Political Gerrymandering and the Courts 213-214 (B. Grofman ed. 1990) (noting that gerrymandering can produce "high proportions of very safe seats")).
76 In their Brief in Jackson v. Perry, at p. 47
77 In their Brief in Jackson v. Perry, at 46-47
78 Whatever might be our views as citizens, as social scientists, we deliberately chose not to advocate a specific threshold test for egregious partisan gerrymandering, since we regard setting this threshold as a matter of constitutional interpretation best left to the courts.
79 In their Brief in Jackson v. Perry, at p. 46
80 The courts have frequently made use of statistical concepts adapted from the social sciences in devising voting rights standards, e.g., Thornburg v. Gingles, 478 U.S. 30, 55-61, 74-77 (1986) (using statistics to determine the existence of racial bloc voting, a necessary part of any § 2 claim); or Brown v. Thomson 462 U.S. 835 (1983) (measuring the total population deviation to adjudicate one person, one vote claims).
81 Vieth, 541 U.S. 267 at 307-308 (Kennedy, J., concurring in the judgment).
82 Davis v. Bandemer, 478 U.S. at 124.
83 See, e.g., Karcher v. Daggett, 462 U.S. 725, 740-41 (1983).
84 Id. at 730.
85 Id. at 730-31
86 Cf. id. at 740.
87 Cf. Thornburg v. Gingles, 478 U.S. at 44-46 (imposing a test for justiciability under § 2 of the Voting Rights Act, 42 U.S.C. § 1973, that requires a showing that the minority population is “sufficiently large and compact to constitute a majority in a single-member district” so there exists a potential remedy plan with at least one more reasonably compact district in which minorities have a realistic opportunity to elect candidates of choice than is found in the challenged plan).
88 Cf. Brown v. Thompson, 462 U.S. 835 (1983) (above 10% population deviation is prima facie unconstitutional for state legislative districts); id. at 852 (outlining test for determining when a plan is unconstitutional).
89 This ten percentage point range threshold would correspond to a bias of five percentage points in that, if one party gets five percentage more and one party five percentage points less than the symmetric outcome, this gives us a difference between the seat shares of the parties (relative to symmetry) of ten percentage points.
90 Cf. Karcher at 733 (noting that in 1983, “[t]he rapid advances of computer technology and education during the last two decades make it relatively simple to draw contiguous districts of equal population and at the same time to further whatever secondary goals the State has.”
91 As far as we are aware, the majoritarian criterion is first proposed -- but not under that name -- in Bernard N. Grofman, Criteria for districting: A social science perspective. UCLA Law Review, (1985), 33(1):77 184, Table 1, p. 174.
92 In Vieth, Justice Breyer has taken a similar view of the importance of majority representation: “At the same time, these considerations can help identify at least one circumstance where use of purely political boundary-drawing factors can amount to a serious, and remediable, abuse, namely the unjustified use of political factors to entrench a minority in power. By entrenchment I mean a situation in which a party that enjoys only minority support among the populace has nonetheless contrived to take, and hold, legislative power. By unjustified entrenchment I mean that the minority's hold on power is purely the result of partisan manipulation and not other factors. These "other" factors that could lead to "justified" (albeit temporary) minority entrenchment include sheer happenstance, the existence of more than two major parties, the unique constitutional requirements of certain representational bodies such as the Senate, or reliance on traditional (geographic, communities of interest, etc.) districting criteria.”
“The democratic harm of unjustified entrenchment is obvious. As this Court has written in respect to popularly-based electoral districts”:
”Logically, in a society ostensibly grounded on representative government, it would seem reasonable that a majority of the people of a State could elect a majority of that State's legislators. To conclude differently, and to sanction minority control of state legislative bodies, would appear to deny majority rights in a way that far surpasses any possible denial of minority rights that might otherwise be thought to result. Since legislatures are responsible for enacting laws by which all citizens are to be governed, they should be bodies which are collectively responsive to the popular will." Reynolds, 377 U.S. at 565, 84 S. Ct. 1362, 12 L. Ed. 2d 506.” (Vieth at 611).
93 Justice Kennedy reports (at p. 4) that “[t]he 1991 plan ‘carefully constructs Democratic districts “with incredibly convoluted lines” and packs “heavily Republican” suburban areas into just a few districts’” Henderson v. Perry, 399 F. Supp. 2d 756 (2005) at 767 n. 47; quoting M. Barone and R. Cohen, Almanac of American Politics, p. 1510 (2003). His opinion notes further that “Voters who considered this unfair and unlawful treatment sought to invalidate the 1991 plan as an unconstitutional partisan gerrymander, but to no avail. See Terrazas v. Slagle, 789 F. Supp. 828, 833 (WD Tex. 1992); Terrazas v. Slagle, 821 F. Supp. 1162, 1175 (WD Tex. 1993). The 1991 plan realized the hopes of Democrats and the fears of Republicans with respect to the composition of the Texas congressional delegation. The 1990’s were years of continued growth for the Texas Republican Party, and by the end of the decade it was sweeping elections for statewide office. Nonetheless, despite carrying 59% of the vote in statewide elections in 2000, The Republicans only won 13 congressional seats to the Democrats; 17. Henderson, supra, at 763.”
94 Also we would emphasize that this test directly involves what we may think of as a special case application of the symmetry standard.
95 Justice Kennedy’s opinion (at pp. 4-6) seems to indicate that he regarded the LULAC challenge to the 2003 Texas congressional plan as failing this test. For example, at p. 5, he quotes the Henderson court’s views that the “practical effect” of the 2001 Balderas court-drawn plan, was to “leave the 1991 Democratic gerrymander largely in place as a ‘legal plan’.” Henderson v. Perry, 399 F. Supp. 2d 756 (2005) at 763. And, as we earlier noted, Justice Kennedy apparently views the 1991 plan, with its perceived perpetuation of a minority party in power, as legally more heinous than what he sees as the 2003’s plan’s exaggeration of the voting strength of a majority party. We would point out, however, that there is dispute about the partisan nature of the 2001 plan. In his opinion (at pp. 5-6), Justice Stevens disputes Justice Kennedy’s characterization of the 2001 plan, and argues that it was, in fact, a politically neutral plan. Thus, in Justice Stevens’ view, the comparison that Justice Kennedy makes between a 2001 plan that is essentially the legacy of a blatant Democratic gerrymander and a 2003 plan biased in favor of Republicans is inapposite. Justice Stevens also quotes extensively to the Henderson court’s characterizations of the 2001 plan, and reminds us (at p. 6) that, at the conclusion of its line-drawing, the Balderas court believed that it had fashioned a map that was “likely to produce a congressional delegation roughly proportional to the party voting breakdown across the state.” App. To Juris. Statement, at 209a. In this context we might note that neither Democrats nor Republicans challenged the Balderas plan as a partisan gerrymander. Justice Stevens (at p. 6) goes on to suggest, however, that insofar as the 2001 plan was biased, the bias was in a pro-Republican and not a pro-Democratic direction. On that page he quotes the Session court for the proposition that: “reflecting the growing strength of the Republican party, the District Court’s plan, 1151, offered that party an advantage in 20 of the 32 congressional seats. See Session, 298 F. Supp. 2d, at 471 (describing 1151C).” Justice Stevens (id.) also quotes the view of the state’s expert in the litigation involving the Balderas plan, Professor Ronald Keith Gaddie, that the Balderas plan was not biased in favor of Democrats, and that it was “‘[m]aybe slightly biased’ in favor of Republicans.” App. 224. Justice Stevens then goes on to note (at p. 6): “In the 2002 congressional elections, however, Republicans were not able to capitalize on the advantage that the Balderas plan had provided them. A number of Democratic incumbents were able to attract the votes of ticket splitters (individuals who voted for candidates from one party in statewide elections and for a candidate from a different party in congressional elections) and thus won elections in some districts that favored Republicans. As a result, Republicans carried only 15 of the  districts drawn by the Balderas court.” In the footnote following (n. 9 at pp. 6-7) Justice Stevens further observes: “It was apparently these electoral results that later caused the District Court to state that the practical effect of Plan 1151C ‘was to leave the Democratic party gerrymander largely in place’” Henderson at 768 n. 2 – the language quoted in Justice Kennedy’s opinion. But in that footnote Justice Stevens goes on to further argue that “the existence of ticket-splitting voters hardly demonstrates that plan 1151C was biased in favor of Democrats.” The apparent factual disagreement between Justice Stevens and Justice Kennedy reflects the different ways in which each treated incumbency advantage. In effect, the analyses relied on by Justice Stevens looked at the plan as if all seats were open seats, while Justice Kennedy paid attention to the effects of Democratic incumbencies in seats that might otherwise be held by Republicans. The JudgIt program allows courts to evaluate plans either with or without taking incumbency advantage into account. Which is the correct approach in our view is ultimately, a legal judgment. However, we would note that incumbents may retire or be swept away by a strong electoral tide if their safety margins are cut too thin. (See B. Grofman and T. Brunell, “Art of the Dummymander,” 2005 op cit.
96 See Richard G., Niemi, Bernard Grofman, Carl Carlucci and Thomas Hofeller. 1990. Measuring compactness and the role of a competent standard in a test for partisan and racial gerrymandering. Journal of Politics, 52(4):1155 1181.
97 Cf. Hofeller, Thomas and Bernard Grofman. 1990. Comparing the compactness of California congressional districts under three different plans, 1980, 1982 and 1984. In Bernard Grofman (ed.), Political Gerrymandering and the Courts. NY: Agathon Press, 281 288.
98 SeeVieth, 541 U.S. at 316 (Kennedy, J., concurring in the judgment).
99Andrew Gelman & Gary King, Enhancing Democracy Through Legislative Redistricting, 88 Am. Pol. Sci. Rev. 541, 546 fig. 2 (1994) (showing 15 states over a twenty-year period where the partisan bias rarely exceeded 5% and never exceeded 10%); Robert X. Browning & Gary King, Seats, Votes, and Gerrymandering: Estimating Representation and Bias in State Legislative Redistricting, 9 Law & Pol. 305, 318 (1987) (examining the Indiana plan in the 1980s that was the subject of Davis v. Bandemer and concluding that the House plan had a bias of 6.2% while the Senate plan had a bias of 2.8%); King & Browning, Democratic Representation, 81 Am. Pol. Sci. Rev. at 1262 Fig. 5 (showing bias in all States, with the plurality showing little if any bias, the vast majority falling within 5 percentage points, a few between 5 and 10, and even fewer above 10); id. at 1269 (listing bias figures for all States and showing only one State with a bias of above 10 percentage points); Gary W. Cox & Jonathan N. Katz, Elbridge Gerry's Salamander: The Electoral Consequences of the Reapportionment Revolution 57-59(2002) (finding extreme cases of gerrymandering at as much as 8 percentage points). We might also note that in the supposedly bipartisan gerrymander Connecticut in the early 1970s that was at issue in Gaffney v. Cummings, 412 U.S. 735 (1973), Gary King, Representation through Legislative Redistricting: A Stochastic Model, 33 Am. J. Pol. Sci. 787, 814 (1989) finds partisan bias of 3%.
100 See, e.g., Shaw v. Reno, 509 U.S. 630, 646-49 (1993) (explaining how to decide whether a race is a preponderant motive, and examining “appearance,” among other factors), and Georgia v. Ashcroft, 539 U.S. 461, 480 (2003) (discussing the concept of minority influence and noting that “[t]he ability of minority voters to elect a candidate of their choice is important but often complex in practice to determine”).
101 While our expertise is primarily in the social sciences, because we each have served as expert witnesses in many situations where we must use our social science knowledge to address legal issues, in this section we propose several different ways in which the Supreme Court might draw upon the concept of partisan bias to craft a constitutional standard for partisan gerrymandering. We do this by looking at how the Court has already successfully crafted judicially manageable standards in other areas of voting rights.
102 462 U.S. 835 (1983).
103 Our discussion of threshold standards in this previous section focused primarily on the first part of the four part test for one person, one vote violations laid down in Brown v. Thomson 462 U.S. 835 (1983) from which we quote above, namely the part which establishes a threshold for identifying a potential one person, one vote constitutional violation.
104Vieth, 158 L. Ed. 2d, at 565. See Bernard Grofman, “Criteria for Redistricting: A Social Science Perspective,” 33 U.C.L.A. Law Review, 77 184 (1985: 88-93)