How much partisanship is too much? Efficiency gap gauges it

To say there is an “efficiency gap” between two people is a wonky way of claiming one person is more productive than another at work. Perhaps one has an advantage of better tools.

That’s essentially what’s being measured by a new mathematical formula that calculates the “efficiency gap” between political parties in elections. The formula determines which party is more efficient at translating votes into victories, and it’s being cited in a high-profile court case from Wisconsin to help measure whether political gerrymandering gives one party an unfair advantage.

Since its creation a few years ago, the efficiency gap has been embraced as “corroborative evidence” by a federal appeals court panel that ruled that Wisconsin Republicans intentionally drew district boundaries for the state Assembly to the disadvantage of Democrats. The U.S. Supreme Court has agreed to hear arguments on that case. If upheld, it could set a nationwide precedent for determining when partisan gerrymandering crosses the line into an unconstitutional infringement on voters’ rights to representation.

The Associated Press used a version of the efficiency gap formula — developed by University of Chicago law professor Nick Stephanopoulos and researcher Eric McGhee of the nonpartisan Public Policy Institute of California — to analyze the results of the 2016 U.S. House and state House or Assembly elections.

WHICH RACES WERE EXCLUDED?

U.S. Senate elections were excluded because they are held on a statewide basis, so gerrymandering would not apply. State senate elections and North Dakota House elections also were excluded because they do not happen all at once, and thus the results would span multiple elections.

Following the researchers’ methodology, the AP looked only at votes cast for Republicans and Democrats, because independent and third-party candidates receive a relatively small portion of the overall vote. This meant a few state house districts — one in Rhode Island, two each in Alaska and Maine, and seven in Vermont — were excluded from the analysis because they were won by independents. Nebraska’s state legislative elections were left out because all candidates run on a non-partisan basis.