AP analysis indicates Idaho district lines favor Republicans

The nationwide study categorized the outcomes of all 435 U.S. House races and about 4,700 state House and Assembly seats, including Indiana's 100 House seats and nine congressional races up for election past year.

The AP also calculated efficiency gap scores for the U.S. House elections, though experts caution those measurements are less statistically meaningful in states with few districts. 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.

Republicans won 64 out of 100 seats, giving them a majority for the first time in almost 100 years. The formula essentially measures and compares each party's wasted votes — those going to the victor in excess of what's needed for victory — in an election and shows that Virginia's GOP votes are more efficiently spread out than Democratic votes.

Redistricting produced dramatic changes in other states. 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.

Democrats held a partisan advantage in races in Maryland, Colorado, and Nevada, the analysis found, where legislative districts were re-drawn by a Democratic-majority legislature, a Democrat-led commission and by a court, respectively. Currently, the 11-person reapportionment panel consists of party leaders in both legislative chambers, three gubernatorial appointees and four by the Supreme Court chief justice.

But "part of it is the gerrymandering issue, in that districts are simply drawn in such a way that it is very difficult" for Democrats to win in many parts of the state, Beatty added. As of last week, there were 221 Republicans in the New Hampshire House, 170 Democrats and two Libertarians. New Hampshire has only two districts, both of which were won by Democrats.

A previous efficiency gap analysis conducted by Simon Jackman, a former professor of political science and statistics at Stanford University, found that the Republican advantage was even higher in the 2012 and 2014 Missouri House elections. And they moved Republican-performing areas into closely divided districts held by Republican incumbents.

The AP's analysis was based on a formula developed by University of Chicago law professor Nick Stephanopoulos and Eric McGhee, a researcher at the nonpartisan Public Policy Institute of California.

Republicans won 64 seats, taking them from a 47-seat minority to a super majority. And other factors beyond partisan gerrymandering could explain the efficiency gap in Kentucky's election, including shifting political attitudes, voters moving to other districts and the quality of candidates.

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.

The national Republican State Leadership Committee, the force behind the party's surge in state legislative elections, attributes its victories to candidates who better represent their communities.