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INTEREST OF AMICI CURIAE 

Amici are forty-four scholars of election law, scientific evidence, and empirical legal methods at law schools and universities throughout the United States. We have no personal interest in the outcome of this case (except to the extent that it may affect our electoral influence as individual voters), but we have a professional interest in seeing that the law relating to the application of scientific and statistical evidence develops in a way that supports and encourages methodologically sound practices.

SUMMARY OF ARGUMENT 

The Panel adopted, and found Act 43 liable under, a three-pronged test for unconstitutional gerrymandering that prohibits any "redistricting scheme which (1) is intended to place a severe impediment on the effectiveness of the votes of individual citizens on the basis of their political affiliation, (2) has that effect, and (3) cannot be justified on other, legitimate legislative grounds." Whitford v. Gill, 218 F.Supp.3d 837, 884 (W.D. Wis. 2016). In the course of factfinding, the Panel weighed and drew inferences from an extensive corpus of scientific and statistical evidence in the trial record. This brief highlights and explains methodologically sound practices for statistical, causal, and predictive inferences in the Panel's adjudication of the discriminatory effect and justification prongs. Amici file this brief in support of plaintiff-appellees because we conclude that the Panel admitted and weighed the relevant evidence without abusing its discretion or committing clear error, and the record of this case provides substantial support for each of the Panel's inferences and findings. 

Part I addresses the justification prong by explaining how the computationally intensive nature of the modern redistricting process makes it amenable to judicial scrutiny through the lens of decision science. Despite the general conceptual difficulty of separating mixed motives, the Panel's findings bring to light a disjunction between (1) the Act 43 drafters' pursuit of partisan objectives in generating alternative maps and (2) their consultation of feasibility constraints when checking these maps for compliance with traditional districting principles. This disjunction yields, in computational terms, the determination that the drafters applied political classifications in a way unrelated to any legitimate legislative objective. 

Part II characterizes the Panel's analysis under the discriminatory effect prong as a causal determination entitled to deference on appeal and premised on interrelated causal and predictive claims. The causal claim is that partisan considerations in the drafting of Act 43 were a substantial cause of the Republican partisan advantages observed in the 2012 and 2014 election results. The predictive claim is that given the extent of the partisan advantages observed in 2012 and 2014, Republicans will likely continue to enjoy a partisan advantage for the life of Act 43. The Panel properly reviewed and drew valid inferences from the scientific and statistical evidence concerning both of these claims. 

While amici believe the Panel's three-pronged test provides an appropriate framework for the constitutional adjudication of partisan gerrymandering claims, the scope of this brief is limited to explaining why the Panel's factual determinations with respect to the discriminatory effect and justification prongs of this test abundantly warrant affirmance.