The judge overseeing Utah’s redistricting now faces a decision whether to stop the state's new law dictating how congressional maps are tested for partisan favoritism.
It’s one piece of Utah’s unusual mid-decade redistricting story, which has only grown more complicated since an August court order threw out the state’s congressional map. And what Third District Court Judge Dianna Gibson decides about these fairness tests will have implications for her highly anticipated ruling on what congressional boundaries Utah will use in 2026.
The law (SB1011) passed by the Legislature in an October special session outlines three measures to determine whether a proposed congressional map unduly favors a political party. State lawmakers also codified that Gibson has to use these tests to evaluate the maps currently before her. If Gibson enjoined – or halted – the law, as plaintiffs are requesting, she’d be able to use other metrics to determine if a map is unfair.
The tests are called ensemble analysis, the mean-median difference test and the partisan bias test. The last of those tests has come under particular fire as problematic to use in Utah.
Arguing before Gibson Nov. 4, attorneys for the League of Women Voters of Utah, Mormon Women for Ethical Government and a handful of Utah voters, said the “cherry picking” of those specific metrics takes away the teeth of Proposition 4, the state’s 2018 citizen-approved ban on gerrymandering at the center of this fight.
The Utah Supreme Court ruled last year in this case that lawmakers acted unconstitutionally when they passed a different law significantly altering Prop 4. Plaintiffs are accusing lawmakers of doing the same thing again.
Conversely, the Legislature’s attorneys said Prop 4’s redistricting standards need the three tests to even have teeth.
Plaintiffs’ attorney Aseem Mulji said that these specific tests are not appropriate in Utah because they create “strange and paradoxical results” that favor the majority party.
“This is so widely recognized in academia that it has a name,” Mulji said of the partisan bias test. “It's called the ‘Utah Paradox.’”
The partisan bias test relies on a hypothetical scenario where both Republicans and Democrats get 50% of the vote. It looks at whether both sides are treated the same in terms of the number of seats they would get.
That hypothetical is far from reality in Utah, where one party usually dominates statewide races. Multiple academics have said maps with four Republican seats are deemed fair by that test, but maps with one Democratic seat are labeled a Republican-favoring gerrymander.
When combined with the mean-median difference, Mulji argued, those two act as “a partisan filter to disqualify any map that doesn't sufficiently crack the state's concentrated democratic population into multiple districts. Again, fighting the state's inherent political geography and the application of Prop 4’s neutral criteria.”
The ensemble analysis creates thousands of computer-generated maps to compare with the proposed map and see if it's an outlier. The problem, however, is that under the Legislature's new law, any maps that fail the partisan bias test are taken out of the comparison set. Mulji argued that defeats the purpose of even doing this kind of analysis.
Outside the courtroom, Mulji told reporters that these tests are “known to produce partisan gerrymanders if in Utah.” The plaintiffs see the Legislature’s test standards, Mulji said, as essentially mandating partisan gerrymandering, which goes against Prop 4.
The state’s central argument is that they were doing their court-directed job in an unusual situation.
Attorney Tyler Green pointed to Gibson’s August ruling, which said the Legislature still had the authority “to determine the ‘best available data and scientific and statistical methods’ to use in evaluating redistricting plans for compliance with state and federal law and the Proposition 4 redistricting.”
Prop 4’s language even includes partisan symmetry in the list of measures for evaluating maps. So, Green said the Legislature picked what they saw as the best measures of partisan symmetry in academic literature.
“At a minimum, there is ample basis in the social science literature to support the Legislature's metrics,” Green said.
If, he said, Gibson finds that both sides have compelling arguments and experts, she should go with the Legislature “for trying to do what this court and what Proposition 4 instructed to do.”
Gibson questioned Green’s argument more than the plaintiffs’. In October’s evidentiary hearings on the submitted maps, she said, hired experts for both sides pointed out that partisan bias should be viewed holistically.
Green responded, “political scientists, when they're doing their work, are not writing laws. They're not doing something that has to be administrable and easily applied.”
It was impossible, Green argued, for the Legislature to pick a test free of disagreement.
In response, Mulji agreed that the Legislature could say which tests it thought were best in this situation, but argued that lawmakers could not enact standards for the judge to use to the exclusion of other metrics.
Gibson said she’ll issue a decision on or before Nov. 10, which is also her deadline for selecting a 2026 map.
