DES MOINES — Lawmakers across the country are protecting themselves by drawing favorable legislative boundaries, according to an Associated Press analysis.

The issue has reached the U.S. Supreme Court, which plans to hear a case involving accusations in Wisconsin of unconstitutional gerrymandering, a process by which lawmakers create political boundaries that condense friendly voters, thus making it easier for them to retain control of a legislative seat.

The AP’s analysis found evidence that political gerrymandering has occurred in almost half of U.S. states.

But not in Iowa.

The AP found both political parties benefitted in states where there was evidence of gerrymandering, although Republicans were helped more often. The AP analysis found four times as many states with Republican-skewed statehouse districts, and nearly three times as many states — among the country’s 12 most populous — with GOP-tilted U.S. House districts.

Iowa was not among the states whose legislative seats were unfairly skewed toward either party.

This comes as no great shock to those who are familiar with Iowa’s process for drawing legislative boundaries; the state’s redistricting procedure has been praised for its neutrality.

Political boundaries are redrawn every 10 years after each new U.S. census. In many states, state legislators draw the new borders. If a political party has complete lawmaking control, that party has some freedom to draw boundaries that benefit its members, making it more difficult to defeat them in ensuing elections.

That process is called gerrymandering.

In Iowa, however, the boundaries are drawn by nonpartisan legislative staff at the Iowa Capitol. They are required to adhere to population and geographical guidelines only; political considerations are not allowed.

Iowa state legislators must sign off on the new maps, but the lawmakers are not directly involved in the maps’ design.

When advocates talk about the need for redistricting reform to curtail gerrymandering, Iowa’s program often is cited.

In 2013, when a pair of Wisconsin state senators — one Republican, one Democrat — called for redistricting reform there, they contrasted gerrymandered legislative districts in Wisconsin (by Republicans) and Illinois (by Democrats) with Iowa’s legislative districts.

“The Illinois and Wisconsin maps illustrate how the redistricting process can be abused. Iowa’s maps show us how redistricting can be done right,” the two state senators wrote in an October 2013 op-ed published by the Capital Times in Madison.

The Associated Press’ analysis appears to support the notion that Iowa’s redistricting process is fair and free of gerrymandering.

The AP applied a formula — developed by a pair of political scientists to detect and quantify gerrymandering — to the 2016 election results for the U.S. House and state legislative races in all 50 states.

The efficiency gap, created by University of Chicago law professor Nick Stephanopoulos and researcher Eric McGhee of the Public Policy Institute of California, was cited by a federal appeals court in the Wisconsin case that will be heard by the Supreme Court.

The AP analysis found significant evidence of gerrymandering in roughly two dozen states, where the efficiency gap was in double digits.

Iowa’s efficiency gap for its Statehouse races was just 4.6 percent in the 2016 elections.

Stephanopoulos and McGhee, in a legal review published in 2015, used their efficiency gap to analyze statehouse elections across the country going back to the 1970s.

Iowa’s efficiency gap for Statehouse races over the decades hovered on either side of right down the political middle, always within the threshold Stephanopoulos and McGhee considered to display fair elections. In the 2000s, Iowa’s efficiency gap was near a perfect zero.

Stephanopoulos said Iowa’s efficiency gap for its congressional districts is not relevant because there are only four districts, making the data unreliable. His and McGhee’s analysis, as well as the AP’s analysis of the 2016 elections, focused on the most populous states.

At the congressional level, the states with the highest efficiency gap — the most glaring evidence of gerrymandering — were North Carolina and Pennsylvania among the most populous Republican-skewed states and Illinois among Democratic-skewed states.

At the state level, South Dakota, Michigan, Wisconsin and Florida were the most Republican-tilted states, and Nevada and Colorado skewed heavily to Democrats.

Michigan, North Carolina, Pennsylvania, Wisconsin, Florida and South Dakota all had their legislative districts drawn by Republicans after the 2010 census; Illinois’ were drawn by Democrats.

In Iowa, Republicans for the first time in 20 years have complete control of the state lawmaking process. For at least 2017 and 2018, they possess majorities in both the Iowa House and Senate, and hold the governor’s office.

Might Iowa Republicans be tempted to rewrite Iowa’s laws and change the state’s redistricting process to free themselves to redraw legislative boundaries after the 2020 U.S. Census, in case they still hold their majorities?

Gov. Kim Reynolds, a Republican, said she has had no discussions with her fellow GOP leaders at the Statehouse about changing Iowa’s redistricting process.