WASHINGTON, DC - SEPTEMBER 09: U.S. President Barack Obama (C) meets with (L-R) Senate Majority Leader Mitch McConnell (R-KY), Speaker of the House John Boehner (R-OH), Senate Majority Leader Harry Reid (D-NV) and House Minority Leader Nancy Pelosi (D-CA) in the Oval Office at the White House September 9, 2014 in Washington, DC. Obama and the Congressional leaders met to discuss the Untied States' response to the Islamic State ahead of the president's remarks to the country tomorrow night. (Photo by Chip Somodevilla/Getty Images) Political differences between Democrats and Republicans are increasingly moving to polar opposites, with their political biases spreading into their social lives more dramatically than race or religious differences. (Photo by Chip Somodevilla/Getty Images)

Stanford, Calif. (CBS DC) — Political differences between Democrats and Republicans are increasingly moving to polar opposites, with their political biases spreading into their social lives more dramatically than race or religious differences.

The Stanford University research, “Fear and Loathing Across Party Lines: New Evidence on Group Polarization,” finds that Americans are increasingly divided along political partisanship, which is a stronger factor for bias than that of race. Hostile feelings among Americans were more ingrained in a widening divide between Republicans and Democrats.

The researchers measured racial bias between blacks and whites against negative feelings held between Democrats and Republicans. And while subjects did exhibit racial bias throughout the four-part study, their political biases more strongly affected people’s behavior outside of the voting booth.

“The polarization of the American electorate has dramatically increased,” said Stanford political scientist Shanto Iyengar, whose co-author was Sean Westwood, a post-doctoral researcher at Princeton University. “We show that the level of partisan animus in the American public exceeds racial hostility.”

In one study, researchers examined a game designed to test people’s trust, in which one player was given money and told they could give some, all or none of the finances into the hands of another player. Subjects gave much larger amounts of money to someone who shared their political association.

Partisan attitudes were tested to predict non-political behavior by examining how 1,000 people viewed the resumes of high school seniors competing for scholarships. Documents included racial cues such as “president of the African American Student Association” and others featured politically-tinged prompts such as “president of the Young Republicans.” The findings showed that race mattered, with African-American participants preferring African-American candidates 73 to 27 percent of the time and whites also showing a preference for African-American applicants – although by a significantly smaller margin.

But political bias showed a much larger impact.

Both Democrats and Republicans chose scholarships for applicants in their party about 80 percent of the time – even when the candidate from the other party boasted stronger academic credentials.

“Unlike race, gender or other social divides where attitudes and behavior are constrained by social norms of civility and tolerance – there are no similar pressures to temper disapproval of political opponents. People feel free to say bad things about their political opponents,” Iyengar told Stanford News. “We were particularly surprised at the extent to which party politics has become a litmus test for interpersonal relations. Marriage across party lines is extremely rare.”

The research operated under the assumption that racial hostility is a deeper line of divide than political opposition: “The general agreement that race represents the deepest divide in American society makes racial affect a particularly robust benchmark for the assessment of partisan affect.”

A multitude of recent surveys and polls also reflect a growing political polarization among Americans.

A June survey from the Pew Research Center showed that the overall share of U.S. adults who express consistently conservative or consistently liberal opinions has doubled over the past two decades from 10 percent to 21 percent. Subjects reported partisan beliefs that have intensified since 1994 was collected, with respondents stating that the opposing party’s policies “are so misguided that they threaten the nation’s well-being.”

The 2014 Pew survey found that 92 percent of Republicans are to the right of the median (middle) Democrat, compared with 64 percent 20 years ago. And 94 percent of Democrats are to the left of the median Republican, up from 70 percent in 1994.

Iyengar suggested that one tactic for diminishing the divide between Democrats and Republicans is “greater personal contact between” the two parties with “significant social interventions that enhance the political heterogeneity of neighborhoods and friendship groups.”