22 ALEXANDER v. SOUTH CAROLINA STATE CONFERENCE OF THE NAACP Opinion of the Court that the State would raise a partisan-gerrymandering defense at trial. Dr. Imai’s conspicuous failure to control for party preference is alone sufficient to discredit any reliance on his report, but his report exhibited another serious flaw: it failed to consider “core district retention,” a term that “refers to the proportion of districts that remain when a State transitions from one districting plan to another.” Allen, 599 U. S., at 21. The Enacted Plan retains 83% of District 1’s core, but the average map produced by Dr. Imai’s model scored 69% on the core-district-retention metric—three standard deviations lower. ECF Doc. 323–33, at 5. Dr. Imai’s failure to consider core retention betrays a blinkered view of the redistricting process. Lawmakers do not typically start with a blank slate; rather, they usually begin with the existing map and make alterations to fit various districting goals. Core retention recognizes this reality. Dr. Imai could have controlled for this metric by restricting the core retention in his simulations to at least 83%. His failure to do so here means we cannot rule out core retention as another plausible explanation for the difference between the Enacted Plan and the average Imai simulation. Dr. Jordan Ragusa. As evidence that race predominated in District 1’s design, the District Court also credited a report by Dr. Jordan Ragusa, another expert for the Challengers. Unlike Dr. Imai, Dr. Ragusa attempted to disentangle race from politics, but as we will explain, his analysis has at least two serious defects. First, he failed to account for two key mapmaking factors: contiguity and compactness. Second, he used an inferior method of measuring a precinct’s partisan leanings. We begin with the matter of contiguity and compactness. Dr. Ragusa used three separate models, but none of them controlled for these critical districting factors. Two of his models employed the so-called county envelope approach.

Select target paragraph3