Conservative evangelicals long have been accused of being biased against Mitt Romney because of his LDS faith, and a new poll released Wednesday sheds light on some details of that bias. It also reveals that 50 percent of Americans don't know Romney is Mormon.

With Romney's "Mormon moment" speech scheduled this morning, the poll of 1,200 Americans — and an oversample of 600 Southern evangelicals — done by political scientists at Vanderbilt University could provide the candidate his best barometer yet on what to say and what not to. Many believe his speech could be the deciding factor in the success of his bid for the GOP presidential nomination — particularly among evangelical Christians.

John Geer, distinguished professor of political science at Vanderbilt, told the Deseret Morning News the poll didn't find any particular reason for bias against Romney's faith. As a member of The Church of Jesus Christ of Latter-day Saints, Romney has been peppered for nearly a year with questions about whether he would take orders from LDS leaders in Salt Lake City.

"The data seems to suggest there's not anything in particular about (bias against) his faith" that voters in general key in on. "It's just a lack of information about it at all."

Geer said people who know Romney is Mormon "exhibit far less bias than those who don't. I think people see in Romney — though they may like or dislike him — here's a real quality candidate, and he de-mystifies what Mormons are."

He said Latter-day Saints face "a different kind of discrimination" than people of other faiths. "Even though they are 2 to 3 percent of the population, you have to think about the distribution of where people live," with the highest concentration of Latter-day Saints in the West.

"A lot of people just don't even know a Mormon personally. Because of that, they can create this kind of caricature" based on stereotypes when they have no information to the contrary, he said.

Geer said he expects Romney can lessen some people's concern "by just de-mystifying (Mormonism)," but that simply asking people to be tolerant of his faith based on American ideals of religious diversity isn't enough. "He's got to give them counter-information (to offset hearsay). Otherwise people buy into the stereotypes about polygamy" and other hot-button issues the LDS Church routinely encounters from people who know little about the faith.

Brett Benson, assistant professor of political science at Vanderbilt and a Latter-day Saint, said the poll used a complex measurement to ask respondents to rate Romney on a "feeling thermometer" and then whether they would vote for him or a Christian alternative.

"When we say Romney is a Christian and Mormons say they are Christian," Southern evangelical respondents "become very defensive," Benson said. Simply asking people whether they would vote for a Mormon for president is less accurate, he said, because "people don't want to be labeled bigots."