Analysis: Large efficiency gap in new legislative maps give Republicans ‘enormous edge’

Maps provided by the Campaign Legal Center

The Campaign Legal Center released a partisan analysis of lawmakers’ new redistricting plan and found extraordinarily large efficiency gap that will give “an enormous Republican edge.”

I conclude that both the Proposed House Plan and the Proposed Senate Plan will likely provide a large and durable advantage to Republican voters and candidates in the coming two elections due to the large efficiency gaps likely to be exhibited, even as the statewide vote swings over a range of 10 percentage points. The expected value of the efficiency gap, based on the stat pack released by the State with the draft plans is -11.98% for the Proposed House Plan and -11.87% for the Proposed Senate Plan. By historical standards, these are extraordinarily large figures, revealing an enormous Republican edge.

Lawmakers released new proposed House and Senate maps over the weekend, and the “stat packs” on Monday, which is the demographic information that was used to draw them. Race was not a factor considered, but election data, or partisan advantage, was.

The memo, released Tuesday by Campaign Legal Center Senior Legal Counsel Ruth Greenwood sets out a brief explanation of what the efficiency gap measures, a summary of the data gathered and methods used, and then presents the results of an analyses.

The efficiency gap is one of several tools used to gauge partisan symmetry in districting plans, according to the memo. Partisan symmetry exists when a district map gives political parties an equal opportunity to translate votes for their candidates into legislative seats.

EG analysis involves three steps. First, add up all of the votes each party wastes due to packing and cracking, across all of the races for a particular legislative body. Second, take the difference between the wasted votes cast for each major political party. Third, divide this difference by the total number of votes cast. The resulting percentage measures how much more effectively one party’s voters are distributed compared to the other party’s voters.

Expert analysis indicates that the value of an EG that suggests a partisan skew is likely to be large and durable for state legislative plans if it is greater in magnitude than +/-7%.

Greenwood’s analysis assumes a statewide uniform swing in the vote. In order for there to be a Republican majority in the House, Republicans will only need a statewide vote of 45.7 percent. By contrast, a Democratic statewide vote share of 54.8 percent will be needed to secure a Democratic majority in the House.

In order for there to be a Republican majority in the Senate, Republicans will only need a statewide vote of 46.15 percent. By contrast, a Democratic statewide vote share of 55.15 percent will be needed to secure a Democratic majority in the House.

You can read the full memo here.

There are public input hearings being held across the state beginning at 4 p.m. today, so the maps could change. The maps are required to be submitted to a federal three-judge panel by Sept. 1 for approval.


  1. Craig Hobaugh

    August 22, 2017 at 7:34 pm

    Why not use county lines. With 100 counties it should not be that difficult to work out!
    Will eliminate Interstate areas, and will make it more difficult to manipulate in the future!

  2. Diane Chadwell

    September 2, 2017 at 2:33 am

    Anyone who fosters fair competition would choose a completely independent, non partisan commission to establish voting districts. The partisan games in NC politics is distasteful and frustrating for the average voter. Other organizations in our communities seem to project greater fairness in their actions and policies. Why must the Republican politicians be such bullies who do not listen to the concerns of voters? Could it be that their policy positions are so repugnant that unfair gerrymandering is the only way they can win?

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