The formula is created to detect races where one party might have won or retained seats in the legislature through drawing district lines favorable to the party in power.
The AP analysis also found that Republicans won as many as 22 additional U.S. House seats over what would have been expected based on the average vote share in congressional districts across the country.
That bucks a national trend in which Republicans control two-thirds of all statehouses.
The analysis found four times as many states with Republican-skewed state House or Assembly districts than Democratic ones.
According to the AP analysis, Colorado's Republican congressional candidates won 51 percent of the statewide vote in November to maintain their 4-3 margin.
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.
Democrats have long complained that Republican lawmakers drew unfair lines during the 2011 redistricting process, and say the proof is in plain sight.
In Texas, Republicans gained almost four excess congressional seats compared to projections from a typical votes-to-seats ratio, according to the AP's analysis.
AP also found that the drawing of districts for hundreds of USA and state legislative districts gave Republicans a real advantage.
"The Democrats don't know how to run campaigns; they're awful at it", he said.
Republicans controlled both MI legislative chambers and the governor's office when the maps were redrawn in 2011. In past years, a lack of competition let Republicans pool resources and spend heavily on a handful of competitive districts.
The efficiency gap method was designed by University of Chicago Law professor Nick Stephanopoulos and researcher Eric McGhee at the Public Policy Institute of California. Its analysis showed that although Democrats had a 51 percent to 49 percent vote edge statewide over Republicans, the GOP had a majority in 102 of the new House districts compared to just 61 for Democrats. 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.
"Party control of redistricting is a powerful driver of the efficiency gap".
One of the largest Democratic congressional advantages was in Maryland, where Democrats controlled redistricting.
Calculating partisan advantage will take on new importance when the U.S. Supreme Court considers whether Wisconsin's state Assembly district maps violate Democratic voters' constitutional rights.
Democratic Sen. Matt Jones was a House representative appointed to the 2011 legislative reapportionment committee.