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Of X-Rays, CT Scans, and Gerrymanders

I’m not a doctor, but I think this analogy is sound, and all the more so after today’s oral argument in Gill v. Whitford, the Wisconsin redistricting case in the Supreme Court.

Think of a disease that was undetectable before the development of medical imaging technologies, a type of brain tumor perhaps. It is still very much a disease even if undetectable.

After years of frustration, along comes the invention of a breakthrough medical technology that for the first time permits the detection of some of these tumors.  X-rays didn’t use to exist, but now they can be used to spot some malignant tumors.  And for a while, the only available imaging technology is an x-ray. 

But then CT scans are invented, and MRIs.  They are improved forms of imagining, able to detect tumors more accurately than x-rays.  The disease is the same; just the way to detect the presence of the disease has improved.

I would suggest that in 2004, when the Supreme Court decided Vieth v. Jubelirer, not even the equivalent of x-rays existed to detect a malignant gerrymander.  The absence of appropriate detection techniques did not mean that gerrymanders were not a cancer on democracy.  On the contrary, all the Justices on the Court at the time recognized that they were.  There just was not an available tool by which to identify when redistricting had become pathological. 

After Vieth, social scientists invented a new detection technology, called the “efficiency gap,” and used it to identify the pathology of Wisconsin’s redistricting map at issue in Gill.  The efficiency gap is far from a perfect detection device; that much is clear from the district court’s trial in Gill as well as various social science commentaries on efficiency gap’s technical properties.  It is like x-rays in this respect; imperfect, but still capable of detecting disease in some circumstances.

Since the development of the “efficiency gap,” social scientists have been hard at work on creating improved detection devices. The mean-median test, for example, and computer simulations.  These might be considered the CT scans and MRIs in the field of redistricting.  There has been incredibly rapid progress in this field, maybe even more rapid than with medical imaging. In both fields, there are likely to be even better techniques in future.  Still, all the while the definition of the disease to be detected remains constant.

What struck me from reading the transcript of today’s oral argument were two points. First, there remains virtually no dispute about the nature of the disease.  As the two attorneys defending Wisconsin’s map both conceded, if there were no issue of detection involved—if the malignant cancer were on the surface of the body politic, so to speak—there would be no doubt about its unconstitutionality.  In response to Justice Kennedy’s question (page 26) about an explicit state rule “that’s saying all legitimate factors must be used in a way to favor party X or party Y,” the Wisconsin legislature’s lawyer (page 27) said “Yes.  It would be unconstitutional,” and the state’s Solicitor General agreed (page 63).  Thus, the only issue is whether the current status of available detection devices permits identification of malignancies that are not on the surface in the same way.  

Which leads to the second point about the oral argument.  

There was considerable use of the term “outlier” to define a gerrymander that would be subject to judicial invalidation.  Justice Breyer (page 12) included the concept as a key component of his effort to articulate a judicially workable test: after identifying whether a map drawn by a partisan legislature was demonstrably skewed against a party, the trial court would ask: “is this an extreme outlier with respect to asymmetry?” Justice Kagan (page 49) asked the plaintiffs’ attorney: “Mr. Smith, are you suggesting that we should be looking for outliers or are you suggesting that we should be trying to filter out all manner of partisan consideration, or is it some place in between?” Mr. Smith’s response (page 50): “Your Honor, the word ‘outlier’ is probably an appropriate one.” Then, confirming this initial thought, he added: “Certainly, we don’t think … that all partisanship is unconstitutional.  What you need is a method by which the extreme gerrymander . . . can be identified and held unconstitutional.”

This focus on the concept of an “outlier” map seems to me important with respect to both understanding the relevant constitutional standard for judges to enforce as well as developing the measurement technique used to enforce the standard.  The very word “outlier” entails a distinction between norm and deviation.  That distinction makes sense in terms of the role that partisan politics is entitled to play in the redistricting process.  Normal partisanship is routine and constitutionally unobjectionable.  It poses no First Amendment problem.  It is a symptom of healthy, competitive democratic contestation between political parties in a free society governed by First Amendment values.  But just as normal cell growth in a human body can turn malignant, so too can normal partisan contestation metastasize into malignant gerrymandering.  The constitutional value at stake, rooted in First Amendment freedom, is to protect the norm from this kind of malignant deviation. 

This basic conceptual distinction between norm and outlier serves to answer a major question raised by Chief Justice Roberts (and echoed by others, including Justice Gorsuch).  “It is just not, it seems, a palatable answer to say the ruling was based on the fact that EG [efficiency gap] was greater than 7 percent,” the Chief Justice observed. (Page 38.)  Then, he added, crucially: “That doesn’t sound like language in the Constitution.” His concern, obviously, is with the apparent arbitrariness of such an efficiency gap cutoff and, most significantly, how to link that cutoff with a governing constitutional principle.  His concern, it must be noted, is one reason why the efficiency gap is just an early-generation detection technique, like an x-ray, most likely to be superseded by the rapid development of improved detection techniques. 

To answer the Chief Justice’s question, the judicial task—as required by First Amendment principles—is to distinguish between, on the one hand, normal partisan redistricting that is reflective of healthy democratic competition from, on the other hand, the pathology of extreme gerrymandering by which one party has subverted the electoral competition between differing political ideas.  That judicial task does not require identifying a cutoff in terms of an amount of partisan asymmetry in a map.  Instead, it requires identifying a map that is outside the norm of politically plausible maps for a given state. 

How then to identify whether or not a map is an outlier in this way?  That is where the development of the latest detection techniques is relevant, and some of these advances have been made even after the trial of Gill itself. Without delving into all the technical details here, these latest developments use increased computing power to build upon a basic statistical insight, that of a so-called “normal distribution” in which a random sample of data will tend to cluster around a mean, the shape of a familiar “bell curve,” with the norm being the area under the curve, and the outliers being the two “tails” of the curve.  This technique can be used to detect whether a state’s actual map is within the norm, or instead is an outlier in the tail of the distribution.  This inquiry is not arbitrary in the way that a 7 percent cutoff in an efficiency gap score arguably is; rather, it is directly tied to the First Amendment distinction between norm and deviation in the operation of healthy partisan contestation.

As I’ve discussed previously, one of the amicus briefs in Gill that most lucidly elucidates the statistical ideas of norm and outlier was submitted by Eric Lander, a molecular biologist and founding director of the Broad Institute at MIT and Harvard.  It is noteworthy that this Lander brief was mentioned twice in today’s oral argument: once by Justice Breyer (page 12) as part of his invocation of the outlier concept; and the other time by the plaintiffs’ attorney, Paul Smith (page 56), agreeing that its distinction between norm and outlier will become central to the constitutional inquiry: “I think it will become part of how these cases are decided.” 

When I first read the Lander brief, I thought it somewhat surprising that the most significant amicus brief, of the multitude submitted, might have been by a molecular biologist, rather than by someone specializing in politics.  But since it turns out that the task here is to distinguish between healthy and malignant redistricting, so that the cancer of extreme gerrymandering does not destroy the body politic, perhaps it is not surprising after all.

Edward B. Foley is Director of the Election Law @ Moritz program. His primary area of current research concerns the resolution of disputed elections. Having published several law journal articles on this topic, he is currently writing a book on the history of disputed elections in the United States. He is also serving as Reporter for the American Law Institute's new Election Law project. Professor Foley's "Free & Fair" is a collection of his writings that he has penned for Election Law @ Moritz. View Complete Profile


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