Washington (CNN)The percentage of Christian voters who cast ballots this year was down compared to other recent midterms, while the percentage of voters who identify as religiously unaffiliated was up.
How the religious makeup of the electorate changed in 2018
This year's election was the first midterm in more than a decade that Christians other than Catholics -- Protestants and "other Christians" -- made up less than half of all voters, according to exit poll data analyzed by Pew.
RELATED: See the full exit poll results.
In 2006, 55% of Americans who voted in US House races were Protestant or other Christian. This year, that figure has fallen to 47%. Another 26% identified as Catholic.
In the same time period, the percentage of religiously unaffiliated voters -- voters who identify as atheist, agnostic, or as not having a religion -- has risen from 11% to 17%.
This trend mirrors the rise of religiously unaffiliated in the country. The number of Americans who identified as not having a religion rose to 55.8 million in 2015, an increase of more than 19 million in eight years, Pew data found. It also has an effect at the ballot box.
Protestants and other Christians have voted Republican in midterms more than other religious groups over the past 12 years, Pew's survey shows, and that trend continued in 2018. According to CNN's exit poll, 56% of Protestants and other Christians voted Republican in House races. Among the other religious groups polled -- Catholic, Jewish, other and no religion -- at least half voted for Democrats. The 2018 exit poll found 42% of Protestants and other Christians voted for Democrats.
Voters with "no religion" voted 70% for Democrats and 28% for Republicans.
Both Democrats and Republicans have been their percentage of religiously unaffiliated party members rise over the years, but Democrats have seen a larger increase, according to Pew. They made up 13% of Republicans and Republican leaners in 2017, compared to 33% of Democrats and Democratic leaners.
About 70% of Americans identify as Christian, including Catholics, Protestants, and members of the Church of Jesus Christ of Latter-day Saints, also known as Mormon. The largest Christian group in the US is evangelicals, who made up about 25% of the population.