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.