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 examined the share of votes cast for Republican and Democratic candidates in each district and projected the expected number of seats each party would gain if districts were drawn so that neither party had an overall advantage.
A nationwide analysis by The Associated Press shows lawmakers can cause some statehouses to skew more Democratic and others more Republican by redrawing political boundaries to cluster or divide certain groups of voters.
The AP report singled out Michigan, North Carolina, Pennsylvania, Wisconsin, Florida, and Virginia as examples of battleground states where Republican-led redistricting after the 2010 census led to a large GOP advantage in elections for the U.S. House and state legislatures. 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. Among the two dozen most populated states that determine the vast majority of Congress, there were almost three times as many with Republican-tilted U.S. House districts.
Likewise, he said state Senate maps are drawn fairly, but Democrats underperform in districts they should win.
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.
"Gerrymandering can't keep you in power if the winds of political change are against you", said University of Kentucky election law and voting rights professor Joshua Douglas. "We met the criteria the Supreme Court required us to meet". The analysis suggests there was a slight Republican advantage in the 2016 election produced by the redistricting in 2011 of the state's seven seats.More news: 42 killed in multiple blasts and firing in 3 Pakistani cities
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After the November election, 59 Republicans control the Idaho House, which has 11 Democrats.
Republicans control both legislative chambers and hold all statewide offices. 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. In past years, a lack of competition let Republicans pool resources and spend heavily on a handful of competitive districts. The efficiency gap scores show Republicans picked up at least two excess seats each in MI and North Carolina. "Their problem is weak candidates who run poor campaigns based on bad ideas, not the districts", said House Speaker William J. Howell spokesman Christopher West.
One of the largest Democratic congressional advantages was in Maryland, where Democrats controlled redistricting.
The AP used their method to calculate efficiency gaps for all states that held partisan House or Assembly elections for all of their districts in 2016.
"That's just a baseless supposition to blame that all on line-drawing", he said.
A map of congressional districts drawn by Pennsylvania's Republican-controlled Legislature helped the GOP win almost three more of the state's U.S. House seats than the party otherwise would have won in last year's election, an Associated Press analysis found.