The efficiency gap is a measure to determine the fairness of electoral districts for first-past-the-post voting with a two-party system.
[1][2] The efficiency gap was first devised by University of Chicago law professor Nicholas Stephanopoulos and political scientist Eric McGhee in 2014.
If the gap exceeded 7%, then Stephanopoulos and McGhee argued that this could allow the party with fewer wasted votes to control the state for the duration of the validity of the map.
In the 2012 election for the state legislature, Republican candidates had 48.6% of the two-party votes but won 61% of the 99 districts.
The court found that the disparate treatment of Democratic and Republican voters violated the 1st and 14th amendments to the US Constitution.
For the State Assembly, 54% of the popular vote supported Democratic candidates, but the Republicans retained their 63-seat majority.
Mira Bernstein raised suggestions for improvement for the current efficiency gap (EG) equation.
A state with 60% of its residents belonging to a single party and an election that awarded 60% of the seats to that party—in other words, a perfectly proportional outcome—would therefore be labeled as problematic vote, because its Efficiency Gap would be
We hope that the Supreme Court agrees with them in a decision that leaves room for EG to pave the way for refined metrics and methods in the years to come.Normalizing EG to a particular proportional split in the population will correct this.