How is it that Republicans and Democrats can split the vote about equally in races for Congress and state legislatures, yet the GOP wins significant majorities in the House of Representatives and in statehouses across the country? Partisan gerrymandering, which manipulates legislative districts for one party’s benefit, has been suspected, but there has been no way to actually quantify it – until now.

An Associated Press team of David Lieb, Meghan Hoyer and Maureen Linke, applying a new statistical method that calculates partisan advantage, analyzed U.S. House and state legislative races across the country last year and found that redistricting controlled by Republicans had given their party a distinct advantage and one that will be hard for Democrats to overcome in upcoming election cycles.

Their multi-format report – including easy-to-grasp interactives and a trove of localized data – is the Beat of the Week.

AP's “efficiency gap” analysis is designed to detect cases in which one party outperformed the other through gerrymandering.

Conceived by Lieb, a Missouri-based member of the AP’s State Government Team, the story did something no one else has attempted. The AP scrutinized the outcomes of all U.S. House and about 4,700 state House and Assembly seats up for election in 2016. The “efficiency gap” statistical method Lieb used is designed to detect cases in which one party may have won, widened or retained its grip on power through political gerrymandering.

The analysis found four times as many states with Republican-skewed state House or Assembly districts as Democratic ones. Among the two dozen most populated states that determine the vast majority of Congress, there were nearly three times as many with Republican-tilted U.S. House districts. Traditional battlegrounds such as Michigan, North Carolina, Pennsylvania, Wisconsin, Florida and Virginia were among those with significant Republican advantages in their U.S. or state House races. All had districts drawn by Republicans after the last Census in 2010.

The constitutionality of partisan gerrymandering is at issue in a case before the U.S. Supreme Court this fall, with a decision due before the next round of redistricting following the 2020 Census. If partisan gerrymandering “goes unchecked, it’s going to be worse – no matter who’s in charge,” said one academic source quoted in AP's story.

The reporting task was daunting. “Gathering and cleaning up the election data for thousands of state house races around the country was a big undertaking,” Lieb said. And that was just the start.

Lieb worked with the researchers who developed the efficiency gap method and did the math and computations for the project. Hoyer, a Washington, D.C.-based data journalist, fact-checked and coordinated distribution to AP members.

The package was part of a planned year-long examination by the State Government Team of how gerrymandering affects democracy.

“The webinar we hosted was one of our most successful – we worked a long time to fine-tune our explanation of the concept (this helped guide tweaks to the stories, as well), and members really got it by the end, asking great questions,” Hoyer said.

Hoyer also worked with Linke, an interactives producer in Washington, D.C., to determine the best way to visualize the complicated subject. Fine-tuning ideas discussed in their meetings, Linke created a chart with contextual elements and pop-up boxes that let readers easily make sense of how gerrymandering may have skewed representation in their state or congressional district.

The package was part of a planned year-long examination by the State Government Team of how gerrymandering affects democracy.

Play was phenomenal. The story ranked No. 4 for the week on AP Mobile and appeared on 37 front pages on Sunday and 55 more on Monday. Several used it as a springboard for editorials, including one in the St. Louis Post-Dispatch headlined, “We all lose when gerrymandered districts lead to lopsided representation.”

For applying cutting-edge data analysis and old-fashioned reportorial digging to produce a unique and accessible examination of gerrymandering’s impact, Lieb, Hoyer and Linke win this week’s $500 prize.