As U.S. courts debate gerrymandering — the process of carving up electoral districts to disproportionately benefit one political party — Wes Pegden's work is helping to shape redistricting maps more fairly.
Pegden, an associate professor of mathematical sciences at Carnegie Mellon University, has developed mathematical theorems that can be used to establish rigorously that districtings are gerrymandered. Pegden collaborated on the research with co-authors Maria Chikina (University of Pittsburgh, Computational and Systems Biology), Alan Frieze (CMU, Mathematics) and Jonathan Mattingly (Duke University, Mathematics).
Pegden's first paper on the subject, published in 2017 in the Proceedings of the National Academy of Sciences, formed the basis of expert testimony he gave in a lawsuit brought by the League of Women Voters, which led the Pennsylvania Supreme Court to order a new Congressional map be drawn for the state. The new map was used in the 2018 election. Pegden also testified in a lawsuit in North Carolina that led to the redrawing of the North Carolina House and Senate maps based on more recent mathematical tools developed by Pegden and co-authors.
"What we've been able to do here is take established mathematical objects in probability theory and prove new things about them, which allow us to use these objects to analyze districtings in a statistically rigorous way," Pegden said. "The point is that when our method finds that a district is gerrymandered, a court can be confident that this is an objective conclusion about the extent to which the districting was optimized for partisan bias against the actual set of alternatives, which were available to the mapmaker, rather than a subject judgment based on our intuition for what might be expected."