The NCSL Blog


By Wendy Underhill

US flag as jigsaw puzzleOn Monday, a three-judge federal court struck down Wisconsin’s legislative district maps, which were drawn five years ago during this decade’s redistricting process. Here are three things to know about Whitford v. Gill (formerly Whitford v. Nichol):

First, this decision marks the end of one stage in what is likely to be a lengthy legal contest. The results will be appealed, says the state’s attorney general. Observers say the case is likely to reach the U.S. Supreme Court.  “It’s unprecedented and it isn’t over,” said Wisconsin’s House Speaker Robin Vos.

Second, the case is based on allegations of partisan line-drawing, something that Democratic and Republican majorities are equally likely to do. To date, there has been no legal standard to stop plans that allocate voters among districts for political purposes, although the courts have left the door open for a case that might set a standard. Indeed, partisanship is not addressed in traditional redistricting principles. Rather, most redistricting cases are based on claims of racial discrimination, differences in district populations, or procedural missteps.

Third, the case offered the courts a new standard: A statistical measure to gauge partisanship called “the efficiency gap.” The concept comes from University of Chicago law professor Nicholas Stephanopoulos, as described in “Partisan Gerrymandering and the Efficiency Gap.” The efficiency gap formula calculates how many votes each party “wastes” compared to each other. (A wasted vote is any vote on the winning side that is above 50 percent plus one, or any vote that’s cast on the losing side.)  The idea is that if voters of the minority party, whether Ds or Rs, are either “packed” too tightly into certain districts during redistricting, or spread too thinly in other districts, then the redistricting plan doesn’t treat the parties evenhandedly. And that’s the legal question addressed in Whitford.

Here’s an example from Stephanopoulos’ work to illustrate the efficiency gap concept (from the fourth page of this 70-page article): 

“Take a state with 10 districts of 100 voters each, in which Party A wins 55 percent of the statewide vote (that is, 550 votes). Assume also that Party A wins 70 votes in districts 1–3, 54 votes in districts 4–8, and 35 votes in districts 9–10, and that the remaining votes are won by Party B. Then Party A wastes 20 votes in districts 1–3, 4 votes in districts 4–8, and 35 votes in districts 9–10. Similarly, Party B wastes 30 votes in districts 1– 3, 46 votes in districts 4–8, and 15 votes in districts 9–10. In sum, Party A wastes 150 votes and Party B wastes 350 votes.  The difference between the parties’ wasted votes is 200, which when divided by 1,000 total votes produces an efficiency gap of 20 percent. Algebraically, this means that Party A wins 20 percent (or 2) more seats than it would have had the parties wasted equal numbers of votes."

Simple? No. But then, nothing is simple when it comes to  redistricting. For a legal analysis of this 2-1 decision, see Rick Hasen’s Election Law Blog post.

Wendy Underhilll is NCSL’s program director for Redistricting and Elections. Legal intern Matt Domboski consulted on this post.

Email Wendy

Actions: E-mail | Permalink |

Subscribe to the NCSL Blog

Click on the RSS feed at left to add the NCSL Blog to your favorite RSS reader. 

About the NCSL Blog

This blog offers updates on the National Conference of State Legislatures' research and training, the latest on federalism and the state legislative institution, and posts about state legislators and legislative staff. The blog is edited by NCSL staff and written primarily by NCSL's experts on public policy and the state legislative institution.