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Princeton brief in Rucho v. Common Cause

March 8th, 2019, 5:26pm by Sam Wang


Wesley Pegden of Carnegie-Mellon University, Jonathan Rodden of Stanford University, and I joined forces on an amicus brief (PDF). We offered the court our views on the federal partisan gerrymandering case from North Carolina, Rucho v. Common Cause (this link goes to all the other briefs as well). We describe to the court how the various tests of partisan unfairness fall into two big categories: inequality of opportunity and inequity of outcome. We furthermore describe how the drawing of many alternative maps can do both jobs.

Wesley Pegden is best known in redistricting circles for a theorem he and co-authors published last year regarding the Monte Carlo Markov chain approach. This approach finds many (typically billions) of maps that are made by making small changes to a candidate map. He showed that if the candidate map is most extreme of N such maps, it must be in the O(1/sqrt(N)) range of maps that can be reached by MCMC. He, Moon Duchin, and Jonathan Mattingly (expert in the N.C. case) have all been applying this approach to redistricting with great effectiveness.

Jonathan Rodden has a long history of drawing ensembles of maps. Using older methods, he and Jowei Chen (now at University of Michigan) have used a random-seeding approach to draw hundreds of maps, not related to one another, to explore a wide range of possibilities.

My own contribution to this brief was to point out that despite the proliferation of map-based and simpler numerical-measurement tests, they fall into two big buckets from a legal standpoint: inequality of opportunity and inequity of outcome. That was the subject of our recent prizewinning entry in the Common Cause contest. Examples include lopsided wins (test of opportunity; applies to N.C.) or uniform wins (again a test opportunity; applies to Maryland). MCMC tests both opportunity and outcome.

We were very ably represented by Tacy Flint. She is a former clerk of Richard Posner and of Stephen Breyer, and she led a legal team at Sidley Austin. All in all, it was a dream team of co-authors and counsel. It was a pleasure to work together!

Tags: Redistricting · Supreme Court

3 Comments so far ↓

  • LondonYoung

    Can you share any color on the mix of authors on PEC’s amicus briefs? Prior briefs have involved cooperation with different groups

    • Sam Wang

      I filled out the description with more detail. You can also read a little more about relevant prior contributions of the co-authors in the brief itself.

    • LondonYoung

      This is helpful.
      You guys are going harder core! Looks good.

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