Former president Barack Obama, left, and former attorney general Eric Holder plan to combat gerrymandering. (Getty Images)

Are American legislative districts drawn fairly — or are they tilted to make it easier for Republicans to win? Many observers believe that the answer is that they’re unfair — and believe that the United States needs dramatic reforms in how it draws those districts to ensure that voters aren’t disenfranchised and their voices are indeed heard.

We analyzed how different institutions over the past 45 years have drawn districts — and when the results are most likely to be less gerrymandered. Here’s what we found.

How important is redistricting reform?

Former president Barack Obama and former attorney general Eric Holder are focusing on combating gerrymandering and opposing redistricting plans that make it harder to Democrats to win.

Meanwhile, state and federal courts have been searching for a simple legal standard by which to evaluate gerrymandering.

The efficiency gap proposed in the Whitford v. Gill case offers one potential solution. This measures the number of “wasted” votes — those cast for losing candidates or for winning candidates beyond what was needed to win. All elections contain some wasted votes, but gerrymandered maps may produce more. Next, the measure compares the number of wasted votes from either party relative to all votes cast in the election. A positive difference between these numbers indicates an electoral advantage for the party with fewer wasted votes.

While the courts keep looking for an effective standard, a few states have tried different ways to draw districts that can reduce gerrymandering and improve representation.

One person, one vote

Neglecting shifts in the population can result in districts with drastically different numbers of citizens, which means that some votes carried substantially more weight than the votes of others in neighboring districts. However, a number of states did exactly this until the Supreme Court intervened.

In the mid-1960s, the Supreme Court ruled in Wesberry v. Sanders and Reynolds v. Sims that not accounting for changes in the population within a state violated the Equal Protection Clause of the Fourteenth Amendment and that future redistricting plans therefore must produce districts of equal populations within each state.

Since then, states are compelled to redraw their districts every decade to comply with the “one-person, one-vote” rulings so that each citizen’s vote counts the same. While the Supreme Court imposed the population equality standard, it did not tell states how they had to redraw their districts. Most states leave this to the state legislature. But as a result, members of whichever party is in power tend to draw districts that help them get reelected and stay in the majority.

Not all, however. Some states use different methods for drawing districts, including independent redistricting commissions, state legislative plans, court-imposed plans, and other types of commissions connected to the state legislature.

What kind of body draws the least gerrymandered districts?

In a new paper (ungated), we evaluate what kinds of districts result from different map-drawing institutions. More specifically, we analyzed redistricting principles for congressional district plans from every state for the 1972 through 2012 redistricting cycles, and state legislative districts from this past cycle.

Traditionally, redistricting is supposed to involve compact districts, maintaining continuity with previous districts, and respecting political subdivisions such as cities and counties. Many reformers view these as non-controversial criteria, suggesting that mapmakers should aim for these standards when they create new district maps. We evaluated districts against these principles and determined which kind of institution is more likely to draw districts that adhere to each of the redistricting principles.

1) Compact districts

We used several measures of compactness — and found that independent commissions draw districts that are more compact. Independent commissions aren’t trying to create districts that lean toward one party or another — and therefore draw fewer meandering and sprawling boundaries. Courts also draw more compact districts once they’re brought in by litigation, whether the judges draw boundaries themselves or assign the task to an outside expert.

2) Respect existing political subdivisions

Independent redistricting commissions are also more likely to draw districts that treat cities or towns or counties as particular units, and less likely to split those political subdivisions into parts. In contrast, legislative-drawn maps tend to snake through several cities and counties. The goal of getting a “safe” district for one party leaves citizens confused about which districts they are in. Further, they have a harder time holding their representatives accountable.

3) District continuity

Independent commissions may also do a better job preserving the cores of prior districts — but only for state legislative districts. For U.S. House seats, independent commissions may be tossing aside gerrymandered districts’ cores but may intend to respect the core more in the future. As IRCs draw new districts in future redistricting cycles, it is possible that continuity will increase in congressional districts as well.

In other research we find that commissions or courts also do a better job than state legislatures at creating more competitive district maps. That’s for several reasons. First, some commissions — like Iowa’s — don’t consider where current representatives live. As a result, two incumbents often have to battle for one district — which makes races elsewhere in the state more competitive. Also, there were maps not constructed with the intent of reducing competition, unlike some state legislative plans.

Independent commissions gerrymander the least

Overall, independent redistricting commissions have done a better job at avoiding gerrymandering, as measured by these three traditional criteria. As a result, districts drawn by independent commissions are likely to be less partisan and more competitive than districts drawn by state legislators.

Thirty states are now considering legislation that would create or expand such redistricting commissions. For example, North Carolina’s House Bill 200 would create a “nonpartisan redistricting process.” Georgia’s Senate Resolution 6 would amend the state constitution to create an “independent bipartisan commission instead of the General Assembly” to redraw legislative and congressional districts.

Independent commissions are relatively new, and some questions still remain. For example, how effectively do they provide opportunities for minority voters? However, they seem promising as a way to draw less gerrymandered districts so far.

Ryan D. Williamson is a PhD candidate at the University of Georgia. Find him on Twitter @ryan_dane.

Michael H. Crespin is the associate director of the Carl Albert Center at the University of Oklahoma. Find him on Twitter @MikeCrespin.

Maxwell Palmer is an assistant professor of political science at Boston University. Find him on Twitter @MaxwellBPalmer.

Barry C. Edwards is a lecturer in the department of political science at the University of Central Florida and its undergraduate program coordinator.