Washington Post Analysis: Redistricting commissions draw fairer districts than politicians do

Christopher Warsaw, Eric McGhee, and Michal Migurski | September 27

Over the past year, states redrew congressional and state legislative districts to reflect new census data on the population. In 33 states, politicians drew the new congressional maps, and in 37 states, they drew the state legislative plans. Predictably, this often led to gerrymandered maps that will entrench the dominant party’s power and enable them to win more seats than they would receive if the state’s seats were allocated based on the percentage of the votes each party won.

To avoid partisan gerrymandering, a number of states have taken redistricting away from the legislature and found some other way to draw their maps. In 10 states, redistricting commissions draw the congressional districts; in 12 states, commissions draw the state legislative maps.

For all of these, the goal is to make districts that are fairer, and also more competitive (in other words, that aren’t so tilted in one direction or another that they always elect whoever wins the primary of one party or another). Generally, commissions draw fairer maps, research finds, although evidence has been more mixed on whether they improve political competition.

Commissions drew fairer 2022 maps than the legislatures did

So how successful were commissions in the current round of redistricting? In recent research, we found that commissions achieved both goals: They drew fairer congressional and state legislative maps than state legislatures did, and they drew fewer districts that were a slam dunk for one party or the other.

Here’s how we know. We examined all the redistricting plans for U.S. House and state legislatures using a measure called the “efficiency gap.” The efficiency gap captures whether one party maximizes its seat share by spreading its voters efficiently across many districts while packing the other party’s voters into a few districts that party is guaranteed to win. When the efficiency gap is large, it’s a sign that a political party has gerrymandered the map.

We then looked at how the efficiency gap varied depending on who drew the map, focusing on states with at least three congressional districts where we could more easily measure partisan bias in their districting plan.

Not surprisingly, we found that plans drawn by Democrats were biased toward Democratic candidates, while plans drawn by Republicans were biased toward Republican candidates. In fact, partisans nearly always drew plans that gave their party an advantage when translating votes to seats. Plans drawn by Democrats tended to have about a 10 percent pro-Democratic efficiency gap, while plans drawn by Republicans had a 10 percent pro-Republican efficiency gap. In contrast, we found that plans drawn either by commissions, divided governments or courts were much fairer — with average efficiency gaps that were indistinguishable from zero, meaning that the state’s districts didn’t give an advantage to one party.

We found the same pattern when we compared the new maps to the previous 2011 maps, and to thousands of nonpartisan computer-drawn maps from the ALARM Project, which don’t take politics into account. No matter how we measured it, we found that courts and commissions created maps with less bias than partisan-drawn maps.

Commissions also drew districts that were more competitive

Redistricting commissions also drew more competitive districts. For congressional plans, they drew competitive districts about 10 percentage points more often than those drawn by partisan legislatures. And the commissions drew competitive state legislative seats about 2.5 percentage points more often than politicians did in their maps.

Will more states adopt redistricting commissions?

Of course, politicians are unlikely to adopt commissions on their own. They would rather control the process themselves — and give their party the advantage.

But voters could take this into their own hands, passing ballot initiatives requiring redistricting commissions, as they have in Arizona, Colorado, California, Michigan and Virginia. Oregon may vote on the issue in 2024, and voters in Arkansas, Florida and Massachusetts have the power to put redistricting commissions on their ballots as well. The Ohio chapters of Common Cause and the League of Women Voters are discussing a ballot initiative that would turn its politician-led redistricting commission into an independent, nonpartisan commission.

However, this term, the Supreme Court will hear Moore v. Harper, in which North Carolina’s state legislature is challenging the state Supreme Court’s ability to review the legality of congressional maps and other rules for federal elections. At issue is the so-called “independent state legislature theory,” which argues that the Constitution explicitly gives state legislatures the power to draw congressional districts. If it sides with the North Carolina legislature, the Supreme Court could find most state districting commissions for congressional elections to be unconstitutional.

Striking down redistricting commissions would almost certainly result in fewer fair and competitive elections, our research finds. If fairness and competition are the goals, the country needs more redistricting commissions, not fewer.