CLC Analysis of Efficiency Gaps in Proposed North Carolina Maps Indicate Large Partisan Bias

Ruth Greenwood
Aug 24, 2017
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The North Carolina Senate Redistricting Committee and House Select Committee on Redistricting held public hearings on Aug. 22, 2017, to discuss proposed House and Senate maps that it released to the public on Aug. 19, 2017.

Campaign Legal Center (CLC) has conducted an analysis on the likely partisan implications of each plan and summarized that analysis in the following memo. The goal is to provide a service that is helpful to the committees and the public in understanding the likely effects of the proposed plans.

Read the memo.

The findings of the analysis show that the Proposed House and the Proposed Senate Plan will likely provide a large and durable advantage to Republican voters and candidates in the coming elections due to the large efficiency gap scores.

Additionally, CLC has developed a second memo, which includes, the Covington Plaintiffs' Proposed HOuse Plan and the Covington Plaintiffs' Proposed Senate plan. The conclusion of this memo is that both the Covington Proposed House and Senate Plans will treat voters of both parties in a significantly more equal way than the NCGA Proposed House and Senate Plans, across a range of likely electoral outcomes.

CLC is also part of the litigation team representing the plaintiffs in Gill v. Whitford, a challenge to Wisconsin’s state assembly district lines that was ruled unconstitutional by a three-judge panel in Nov. 2016. The case will be heard by the Supreme Court in October 2017. The Whitford case also uses the efficiency gap as a measure of the partisan asymmetry of redistricting plans.

The efficiency gap is one of several tools that can be used to gauge the level of partisan symmetry in a redistricting plan. Partisan symmetry exists when a district map gives political parties an equal opportunity to translate votes for their candidates into legislative seats. The efficiency gap makes this calculation by essentially identifying all the “packing” (which occurs where a party’s supporters are placed into a small number of districts it will win by overwhelming margins) and “cracking” (which occurs where a party’s supporters are divided into districts where they will narrowly lose) in a district plan. The resulting efficiency gap score indicates how much more effectively one party’s voters are distributed compared to the other party’s voters.

Previous analysis conducted by CLC in January 2017 showed with certainty that the post-2010 redistricting cycle is the most extreme partisan gerrymandering in modern American history. These huge skews favor both Democrats and Republicans, depending on the state.

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