The Executive Suite: Cut Thine Enemy's Cake: A Proposed Redistricting Solution Based on Game Theory

Friday, December 1, 2017

Cut Thine Enemy's Cake: A Proposed Redistricting Solution Based on Game Theory

Recently, professors at Carnegie Mellon University [official website] have proposed a method to reform redistricting and avoid partisan gerrymandering.

The plan [abstract] proposed by the CMU professors would seek to take advantage of each party’s self-interest to create fairer and less partisan maps. In the abstract, the professors call their method “I-cut-you-freeze.” The abstract compares this method to “classical cake-cutting problems" and draws on game theory to prove their redistricting method—where the cake-cutter knows the other “player” is going to pick their preferred piece—is more likely to result in evenly cut "pieces," or districts.

Essentially, if the state legislature is controlled by the Republicans (as is the case in Pennsylvania, for example) then the Republicans would draw all the districts in in the state and then the Democrats would pick the district they preferred and freeze it. Then, they would switch roles. The Democrats would redraw all of the remaining districts according to their preferences and the Republicans would pick their preferred districts and freeze it.

To use the cake metaphor, if the Republicans cut the cake unevenly, then the Democrats could take the largest, most favorable piece available. Thus, it would benefit the Republicans to make slices as even as possible and vice versa.

The professors point out that their proof of the “I-cut-you-freeze” method is carried out in idealized scenarios. Nonetheless, they argue that "the protocol produces a result within reason, and that neither player gains a significant advantage from the choice of who is assigned the first move in the protocol; we expect that both of these properties would persist in real-world applications."

The primary issue with the real-world implementation of this theory is the existence of exterior restraints, like state-imposed geometric restrictions and minority opportunity districts mandated [bill text] by the Voter Rights Act.

Partisan gerrymandering has become an increasingly debated topic in recent years. In most states, legislatures draw congressional districts every 10 years, following a decennial census. This means that the party holding power at census time has primary influence over the choice of districts and potentially outsized representation in future elections.

Increasingly, states have attempted to find solutions to avoid partisan gerrymandering. Some states have created independent redistricting boards comprised of an even number of Republicans, Democrats, and Independents, such as Arizona's Independent Redistricting Commission [official website]. Despite seemingly well-intentioned, non-partisan plans forwarded by such commissions, they have faced criticism and legal challenges [AZCentral report].

The "I-cut-you-freeze" proposal would embrace the natural self-interest of each party and impose procedural restraints to channel that self-interest into less partisan results without an "independent" actor.