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When they're not slinging mud at one another, political candidates love making references to religion. Overt or subtle professions of faith are not limited to Republicans courting Evangelical voters; both Bill Clinton and Barack Obama skillfully incorporated religious allusions into their campaign speeches.

Why all this talk of God? New research suggests it reflects Americans' widespread prejudice against atheists, and belief that the non-religious are less than trustworthy.

"When a candidate is perceived as adhering to a set of religious values, voters see them as moral and possessing high levels of integrity and honesty," write political scientists Scott Clifford of the University of Houston and Ben Gaskins of Lewis & Clark College. "Such perceptions ultimately translate into increased political support for these candidates."

As we have noted previously, Americans are prone to making negative, broad-brush assumptions about non-believers. In the journal American Politics Research, Clifford and Gaskins confirm this by analyzing a Newsweek poll from March 2007, which explicitly asked "Would you vote for a political candidate who says he or she is an atheist, or not?"

"Only 30 percent of the sample answered affirmatively," they note, adding that, among believers, "only Jews are not turned off by an atheist politician."

"Only Evangelicals said that they found atheists less likely to be moral," the researchers report. "Yet despite believing that it is possible for an atheist to be moral, the other religious identifiers express wariness of supporting an atheist for public office."

Clifford and Gaskins also analyzed a 2007 CBS News poll, focusing on attitudes toward Hillary Clinton. Participants were asked whether they were likely to vote for her, whether she has "strong religious values," and whether she "has more honesty and integrity than most people in public life."

"Signaling religiousness can be a powerful tactic for candidates to improve perceptions of their trustworthiness and morality, and to increase their vote share."

They found that "perceived religiousness has a positive significant effect on favorability, increasing the probability of favorable views of Clinton by 20 percentage points." Not surprisingly, the association between religiosity and trustworthiness was higher among conservatives and moderates, which means "expressing religious identity may be a key strategy to broadening her political coalition."

What's more, they found she pays no price for doing so: Even secular liberals are "more likely to view her favorably and vote for her if they see her as religious."

Finally, the researchers conducted an experiment using 311 people recruited on Amazon's Mechanical Turk website. "Our sample was highly non-religious," they note, adding that 48 percent reported never going to church.

Participants read a paragraph describing a fictional political candidate, Jeff Roberts. Some versions of the blurb simply called him "a family man," while others added that he either was an atheist or held "strong religious beliefs." Participants were asked to evaluate him in terms of six character traits, including intelligence and honesty.

The researchers found the highly religious candidate "has the broadest appeal," thanks to the positive perception of his moral character. "The atheist candidate is the most polarizing," they write, "with religious moderates and conservatives viewing him as less moral and trustworthy, and non-religious liberals viewing him as more moral and trustworthy."

That latter group is relatively small—seven percent of Americans, in the 2007 CBS poll—but recent research finds the number of non-religious people is growing. This suggests anti-atheist prejudice may, gradually, subside.

For now, however, "signaling religiousness can be a powerful tactic for candidates to improve perceptions of their trustworthiness and morality, and to increase their vote share," the researchers conclude.

"For Republican politicians, displays of religiousness will likely reinforce preexisting support from those who are predisposed to agree with their policies, while also (unless taken too far) increasing their perceived moral character, honesty, and trust among non-conservatives." For Democrats, they add, "displays of religiousness can serve to expand their appeal among moderates and conservatives without significantly endangering support from liberal votes."

So expect to hear lots of Biblical references, veiled and otherwise, over the next year. As a strategy to get elected, it's a lot more effective than relying on prayer.

Findings is a daily column by Pacific Standard staff writer Tom Jacobs, who scours the psychological-research journals to discover new insights into human behavior, ranging from the origins of our political beliefs to the cultivation of creativity.