In its decision rejecting the legislature’s new congressional map, the Utah trial court included a lengthy discussion of quantitative measures of partisan fairness in districting. The legislature argued that partisan asymmetry and the mean-median difference should be used to assess its new map. The court responded, correctly in my view, that these are exactly the wrong metrics to use in Utah. These metrics are inapplicable in uncompetitive states like Utah, while other approaches, like the efficiency gap and ensemble analysis, do work in Utah’s political environment. The court’s decision is here.
The Court finds that the partisan bias test is unsuitable for assessing whether a redistricting plan in Utah purposefully or unduly favors or disfavors a political party. It is not among the best available measures to assess partisan favoritism in Utah.
First, because partisan bias assesses favoritism based solely on seat shares under a hypothetical 50-50 statewide election, scholars warn that it should not be applied in states like Utah where statewide elections are uncompetitive and a tied statewide election cannot plausibly be expected. The authors of the metric, Professors Andrew Gelman and Gary King, limited its application to “competitive electoral systems,” which they defined as states in which each party had won a majority of seats or votes in at least one election during the preceding two decades. Professor Gary King has since emphasized that partisan bias “is only appropriate for competitive situations where there is a potential for change in partisan outcomes (majority control, in particular).”
The Court finds that Utah’s statewide elections are highly uncompetitive. Democrats have not received a majority of the statewide vote in congressional elections in 35 years and have not won a majority of congressional seats since at least 1970. Republicans have also won every statewide election for president, governor, and other offices included in S.B. 1011’s partisan index during the last 25 years, nearly always with 20-plus margins. Utah’s highly uncompetitive environment also undermines the validity of the partisan bias test’s uniform shift assumption—that is, the assumption that the shift to a 50-50 statewide vote share would occur uniformly across districts. Since this scenario has not even remotely occurred in decades, it is at best unclear how electoral coalitions would shift to produce a 50-50 statewide election and whether the uniform shift assumption underlying the partisan bias test is satisfied in Utah. Thus, Utah does not satisfy the electoral conditions necessary for valid application of the partisan bias test.
Second, when applied in Utah to congressional plans, the partisan bias test yields paradoxical results that advantage Republicans and disadvantage Democrats. The test treats most 3-1 maps that include one Democratic-leaning district as biased in favor of Republicans and against Democrats, because in a hypothetical tied statewide election Democrats would not win two seats. At the same time, it treats 4-0 maps that guarantee Republicans all four seats as neutral. This irrational result stems from the test’s conflict with Utah’s political geography. To pass, a map must disperse Democrats across two districts to ensure they would win two seats in the hypothetical world of a tied statewide election. But because Democrats are a small, geographically concentrated minority, doing so dilutes their only opportunity in the real world to win one seat. . . .
Scholars have recognized this effect as the “Utah paradox”—one that is known to be gameable and the reason why partisan actors in Utah would opt to use partisan bias as their metric to assess congressional plans. Notably, the Legislature applied the partisan bias test only to congressional plans. Utah Code § 20A-19-103(1)(c), (g). The Legislature did not apply the partisan bias test to its own legislative maps or the state school board maps, all of which would fail the test for exhibiting pro-Republican bias. . . .
Unlike the partisan bias and mean-median difference tests—which yield wholly incoherent results in uncompetitive states—the efficiency gap is not inapplicable in a state as uncompetitive as Utah. As Dr. Warshaw explains, the original authors of the efficiency gap acknowledged that the efficiency gap may be inapplicable in states where one party consistently wins more than 75% of the vote, “[b]ut Utah does not fall into that category. So . . . Utah is not outside of the boundary conditions of the efficiency gap.”
The Court finds that, despite its drawbacks, the efficiency gap is an appropriate symmetry measure to consider in assessing congressional maps in Utah. It correctly identifies the party favored under a proposed congressional map and permits analysis of the extent to which that party is favored via comparison with historical congressional plans in other states. The efficiency gap is thus among the best symmetry measures available to evaluate partisan favoritism in Utah congressional maps and should be considered alongside other appropriate measures.
