A New Method For Finding Gerrymandered Districts ?

(These images of gerrymandered districts ate from the National Journal.)

We have a serious problem with political parties gerrymandering congressional (and state legislative) districts in this country. Gerrymandering allows the party in power to make sure they maintain a majority regardless of how the public votes. Some examples of gerrymandered districts are shown above, but not all unfair districts are as obvious as those.

It is gerrymandering that allowed the Republicans in Congress to maintain their majority in 2012, even though they got over a million less votes than Democratic congressional candidates did. The Supreme Court has outlawed gerrymandering, but it continues because it is very hard to prove a district was drawn to be unfair to a particular party. There may now be a simple solution to this problem.

Law professor Nicholas Stephanopoulos and political scientist Eric McGhee have come up with a fairly simple mathematical formula for determining if districts were gerrymandered. It is currently being used in court to attack some gerrymandering in Wisconsin, and it has already survived two court challenges. It will undoubtably wind up in the U.S. Supreme Court.

Here is how Think Progress describes the new formula. What do you think of it? Does it make sense? Should it be used in all states?

Stephanopoulos and McGhee’s central insight is that gerrymanders operate by forcing the disadvantaged party to “waste” votes. Some voters are shunted into districts where their party’s candidate has no chance of winning, a process known as “cracking.” Others are crammed into districts that so overwhelmingly favor their party’s candidate that casting an additional ballot for that candidate merely adds padding to a foregone conclusion, a process known as “packing.” “A gerrymander,” Stephanopoulos and McGhee write, “is simply a district plan that results in one party wasting many more votes than its adversary.”

To sniff out possibly gerrymanders, Stephanopoulos and McGhee begin by counting each party’s “wasted” votes. As the three-judge panel hearing the Whitford case explained in a recent opinion, a wasted vote occurs when a voter either casts a ballot “for a candidate who lost the election” (suggesting that the voter was targeted by cracking), or if they cast a ballot “for the winning candidate, but in excess of what the candidate needed to win” (suggesting that the voter was packed).

As Stephanopoulos and McGhee note, some number of wasted votes are inevitable in elections involving single-member districts. But a fair map should produce roughly equal numbers of wasted votes for both parties. To determine which maps diverge too far from the ideal, the two scholars offer a metric they call the “efficiency gap,” which is calculated by taking the difference of the two parties’ wasted votes and then dividing it by the total number of votes cast. The plaintiffs in Whitford (speaking through a team of lawyers that includes Stephanopoulos) offer an example of how to calculate this figure in their complaint:

Suppose, for example, that there are five districts in a plan with 100 voters each. Suppose also that Party A wins three of the districts by a margin of 60 votes to 40, and that Party B wins two of them by a margin of 80 votes to 20. Then Party A wastes 10 votes in each of the three districts it wins and 20 votes in each of the two districts it loses, adding up to 70 wasted votes. Likewise, Party B wastes 30 votes in each of the two districts it wins and 40 votes in each of the three districts it loses, adding up to 180 wasted votes. The difference between the parties’ respective wasted votes is 110, which, when divided by 500 total votes, yields an efficiency gap of 22% in favor of Party A.

An efficiency gap of more than 7 percent, these plaintiffs claim, is indicative of a partisan gerrymander. When combined with evidence that the state acted intentionally to give one party an advantage, they argue that courts should presume that a map that produces such a high efficiency gap is an unconstitutional partisan gerrymander.