Sam Wang and Brian Remlinger have posted this timely draft on SSRN. Here is the abstract:
The Supreme Court appears ready to limit extreme partisan gerrymanders. However, defining “extreme” is a challenging proposition, since individual states differ in their political geography and legal circumstances. Many measurement tools have emerged that probe the questions of whether a redistricting map is extreme, or violates the principle of partisan symmetry. Here we provide a framework for categorizing these tests. Our framework explains how measures should be interpreted and identifies which tests will be most effective, given the specific facts of a particular state. Broadly, the tests can be divided into two categories: those that identify inequality of opportunity, i.e. a systematic deprivation of one side’s ability to elect representatives; and those that identify inequality of outcome, i.e. a durable distortion in the amount of representation. In each case, the baseline for comparison is what would occur under districting processes in which partisan interests are not the overriding consideration. A general thread is that of “significance testing,” in which a district or statewide districting scheme can be defined as more extreme than the great majority of possibilities that could arise incidentally through a districting process driven by criteria other than extreme partisanship. Such tests are most often done with well-established classical statistical tests, but can also include recently-developed measures such as the efficiency gap. Many of these measures can be evaluated by a judge or clerk, with minimal need for reliance on expert witnesses. It is even now possible to evaluate, with mathematical rigor, whether a specific scheme is extreme relative to the virtually uncountable universe of possible maps. Taken together, these methods for detecting extremes comprise a statistical toolbox to address a wide variety of circumstances that may arise in the post-Whitford, post-Benisek environment.
Really looking forward to diving into this when I can get my head above water.