Created to detect cases in which one party may have secured power through political gerrymandering, it found that the GOP may have won as many as 22 additional congressional seats more than expected.
The analysis found Republicans won 56 percent of the votes in Ohio's Statehouse races but 66 percent of the seats.
When Kentucky Republicans made it a goal to win a majority in the state House of Representatives, they had one obvious disadvantage to overcome: Winning in districts that were drawn by Democrats. Idaho has a 13 percent efficiency gap heavily favoring Republican congressional candidates.
In a recent case challenging North Carolina's congressional districts, political scientist Simon Jackman suggested that an initial election efficiency gap of at least 7.5 percent in a state with more than 15 U.S. House districts should attract scrutiny.
Toscano said opposition to Trump is so strong that it's overcome the reluctance Democratic candidates have had in the past to compete in a district with Republican-friendly boundaries. They said factors other than gerrymandering could have contributed, including shifting political attitudes. "We met the criteria the Supreme Court required us to meet".
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Republican candidates had other advantages, the AP found, from a larger number of incumbents to a voter base spread over more of the country rather than concentrated in cities. That helped provide the GOP with a comfortable majority that stood at 241-194 over Democrats after the 2016 elections - a 10 percentage point margin in seats, even though Republican candidates received just 1 percentage point more total votes nationwide. Despite operating under the bipartisan system since 1992, plans can get caught up in lengthy legal battles before settling on new district boundaries. Chris Jones testified in federal court he tried to accommodate requests from a large majority of delegates, both Republicans and Democrats, who sought to tweak lines, sometimes to draw out precincts where they had historically performed poorly.
Part of the reason may be a political climate of costly, negative campaigns that discourages potential candidates, said Beatty, the House minority leader. While it also showed Florida Republicans' advantage in Congress was slightly more than should've been expected, it wasn't to the point that clearly indicated gerrymandering.
Two researchers who developed the efficiency gap say Kentucky's results are, statistically speaking, not much different than zero. It was the opposite of 2014, when a similar analysis showed Democrats had a slight advantage in the same districts.
For Democrats to complain of gerrymandering is "pure nonsense", said Matt Walter, the Republican committee's president.
The AP scrutinized all 435 U.S. House races from November using a new statistical method of calculating partisan advantage.