A candidate’s religious affiliation has been shown to influence American voters. But a new study reveals that a candidate’s religiosity — meaning how dedicated they are to their faith — also influences voters.

The study in the Journal for the Scientific Study of Religion suggests that voters use a candidate’s religiosity to infer the candidate’s partisanship and his or her positions on cultural issues. The study also suggests that secular candidates face a particular disadvantage.

Jeremiah J. Castle of Central Michigan University, the study’s corresponding author, told PsyPost that he was interested in researching the topic because of the growing importance of religion in American politics.

“Since the 1960s, we have seen the religious differences between the parties to shift from differences based on religious tradition (broadly, what religion people are) to differences based on religiosity (how religious people are),” he explained. “We were interested in what implications this change might have had for American electoral politics.”

“Anecdotally, we know that candidate religiosity has been an important part of the conversation in several recent elections,” Castle explained. “In 2004, some Republicans suggested that Democratic presidential candidate John Kerry wasn’t ‘orthodox enough’ in the way he practiced his Catholic faith. In 2012, Mitt Romney’s campaign downplayed his strong commitment to his Mormon faith. In 2016, Donald Trump did the opposite, heavily emphasizing his religiosity and appearing with well-known Christians like Jerry Falwell, Jr.”

“The fact that religiosity has been so important to both candidates and political observers suggested that we needed to understand the dynamics behind its relationship to party more clearly,” Castle said.

Castle and his colleagues analyzed data from nearly 3,000 respondents who participated in the 2009 Cooperative Congressional Election Study, a national survey.

Respondents were presented with a profile and a brief quote from a fictional state legislative candidate. The candidate’s party was varied to be either Democrat, Republican, or not mentioned. The short quote was varied to be either moderately religious, strongly religious, avowedly secular, or unrelated to religion. The fictional candidate’s purported policy agenda never changed.

“We build a theory that candidates’ levels of religiosity should impact voter support. Specifically, highly religious candidates (regardless of party) should receive greater support from Republicans and cultural conservatives, reduced support from Democrats and cultural progressives, even after accounting for religious differences in the make-up of the party coalitions. The dynamic is the reverse among Democrats: secular candidates should be more attractive to Democrats/cultural progressives and less appealing to Republicans/cultural conservatives.”

The results of the survey confirmed the researchers’ hypothesis. “Overall, we see strong evidence that a candidate’s level of religiosity conditions the impact of party identification and cultural issue attitudes,” Castle remarked.

Being strongly religious increased support among Republicans while decreasing support among Democrats. Being secular, on the other hand, decreased support among Republicans but increased support among Democrats.

“The results have a number of implications for American politics,” Castle said. “First, they suggest that there is still a strong bias against secular candidates. In particular, we saw that Republicans had sharply negative reactions to the secular Republican candidate — in this treatment, the effect of party identification on candidate preference disappeared almost entirely. Second, the dynamics behind the paper suggest that candidates who do not fit their party’s ‘typical’ profile will struggle to get elected. This homogeneity within parties could be one contributing factor to the increasing polarization of the parties in Congress.”

Castle said a major caveat of the study was that respondents were only presented with one candidate at a time. “Thus, we cannot say at this stage how a candidate’s level of religiosity might affect support in a two candidate environment,” he explained. “For example, we saw in our experiment that Republican and conservative voters react negatively to a secular Republican. However, based on our data we cannot say how a secular Republican would fare against a highly religious Democrat. Party identification and candidate religiosity are both clearly strong indicators of candidate preference, so it would be interesting to see which matters more when voters are faced with a tough choice.”

The study, “Survey Experiments on Candidate Religiosity, Political Attitudes, and Vote Choice” was also co-authored by Geoffrey C. Layman, David E. Campbell, and John C. Green.