The study is based on a formula that compares the statewide average share of each party's vote in the districts with the statewide percentage of seats it wins.
The partisan tilt was more than any other state, except for Texas, according to AP's national analysis. That results in a 47 percent efficiency gap heavily favoring Democrats, but both races were close, and if fewer than 5,000 votes had switched in either district, the efficiency gap would be almost even.
The analysis found that Virginia was among those states with Republican-skewed state House districts as well as congressional districts.
Democrats have long complained that Republican lawmakers drew unfair lines during the 2011 redistricting process, and say the proof is in plain sight. For some candidates - such as Republican Rep. Craig Redmon in northeastern Missouri and Democratic Rep. Gail McCann Beatty in Kansas City - 2016 marked the third straight election in which they were the only choice on the ballot. "We met the criteria the Supreme Court required us to meet". An Associated Press analysis found those districts also have produced a consistent Republican advantage that has helped swell the GOP's majority to some of highest levels in state history - higher even than what would be expected based on Republicans' share of the vote. 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.
Republicans controlled both MI legislative chambers and the governor's office when the maps were redrawn in 2011. But they point out Republicans are at this point just better at raising money, recruiting candidates and winning races in districts that should be more competitive.
"Republicans have done a good job of targeting those areas and getting good candidates and putting a lot of money into marginal districts, which they tend to win", he said.
Yet there also were some districts that didn't appear to follow the Republican proposal, said former citizens' commission member Nick Myers, who now is secretary of the Missouri Republican State Committee. The efficiency gap scores show Republicans picked up at least two excess seats each in MI and North Carolina.
"Party control of redistricting is a powerful driver of the efficiency gap". It was the opposite of 2014, when a similar analysis showed Democrats had a slight advantage in the same districts.
"Republicans really put their foot on the gas when Bush got elected", said Steve Schale, a Democratic political consultant.
Republican state Sens. Dan Soucek, left, and Brent Jackson, right, review historical maps during The Senate Redistricting Committee for the 2016 Extra Session in the Legislative Office Building at the N.C. General Assembly, Feb. 16, 2016, in Raleigh, N.C. An Associated Press analysis, using a new statistical method of calculating partisan advantage, finds traditional battlegrounds such as Michigan, North Carolina, Pennsylvania, Wisconsin, Florida and Virginia were among those with significant Republican advantages in their USA or state House races in 2016.