Scott Clifford is an assistant professor of political science at the University of Houston. Credit: Scott Clifford/UH

It's political season and there's one thing you're sure to hear a lot about from candidates vying for support—religion. Talking directly or subtly about religion has become part of the American way in political campaigns.

A new study suggests including religion in campaign speeches feeds a belief that those who are religious to some extent are trustworthy and viewed more favorably. The study was conducted by Scott Clifford of the University of Houston Department of Political Science and Ben Gaskins of Lewis & Clark College.

"Their religious identification reflects a powerful, widespread, but often subtle and unconscious bias in American society against those who do not believe in God," Clifford said. The researchers note that there has been only one openly atheist congressman (Pete Stark, D-California), who lost in 2012.

Their findings were published in the journal American Politics Research.

Clifford and Gaskins say their study shows the challenges for non-religious candidates vying for public office.

Using national survey polling data, the researchers assessed the willingness of voters to support an atheist candidate, the favorability of candidate Hillary Clinton depending on whether she is viewed as religious, and the view that a religious candidate is trustworthy.

"Our findings suggest that not demonstrating religiousness is a significant roadblock for winning public office in the United States, and being perceived as religious increases the level of trust instilled in politicians by voters," Clifford said. "For Republicans (showing religiousness) will reinforce their existing support, but Democrats can expand appeal to moderates and conservatives with displays of religiousness."

Among their findings:

Believing atheists are moral increases willingness to vote for such a candidate

27 percent of respondents said atheists cannot be moral

Majority said they would not vote for an atheist

Mormons were 28 percentage points less likely than those with no religious affiliation to vote for an atheist

Jewish respondents were no more or less likely than those with no religious affiliation to vote for an atheist

Additionally, they found that candidate Hillary Clinton was viewed more favorably and perceived to be more honest if she also was thought to be religious. That view was held most notably by non-liberals, who also indicated they were more likely to vote for her.

Clifford and Gaskins used data from two polls—2007 Newsweek poll of 1,004 adults, 2007 CBS News poll of 1,282 adults.

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