One-fifth of U.S. adults say they are not part of a traditional religious denomination, new data from the Pew Research Center show, evidence of an unprecedented reshuffling of Americans' spiritual identities that is shaking up fields from charity to politics.

But despite their nickname, the "nones" are far from godless. Many pray, believe in God and have regular spiritual routines.

Their numbers have changed dramatically over the past two decades, according to the study released Tuesday. About 19.6 per cent of Americans say they are "nothing in particular," agnostic or aetheist, up from about 8 per cent in 1990. One-third of adults under 30 say the same. Pew offered people a list of more than a dozen possible affiliations, including "Protestant," "Catholic," "something else" and "nothing in particular."

For the first time, Pew also reported that the number of Americans identifying themselves as Protestant dipped below half, at 48 per cent. But the United States is still very traditional when it comes to religion, with 79 per cent of Americans identifying with a traditional faith group.

Experts have been tracking unaffiliated Americans since their numbers began rising, but new studies are adding details to the portrait.

Members can be found in all educational and income groups, but they skew heavily in one direction politically: 68 per cent lean toward the Democratic Party. That makes the "nones," at 24 per cent, the largest Democratic faith constituency, with black Protestants at 16 per cent and white mainline Protestants at 14 per cent.

By comparison, white evangelicals make up 34 per cent of the Republican base.

The study presents a stark map of how political and religious polarization have merged in recent decades. Congregations used to be a blend of political affiliations, but that's generally not the case anymore. Sociologists have shown that Americans are more likely to pick their place of worship by their politics, not vice versa.

Some said the study and its data on younger generations forecast more polarization.

"We think it's mostly a reaction to the religious right," said Harvard political scientist Robert Putnam, who has written at length about the decline in religious affiliation. "The best predictor of which people have moved into this category over the last 20 years is how they feel about religion and politics" aligning, particularly conservative politics and opposition to gay civil rights.

Americans have been fleeing institutions in general, Putnam wrote in his bestselling book "Bowling Alone," about the decline of such institutions as hobby clubs and alumni associations. The culture is also more secular, with prayer in schools and the closing of businesses on Sundays fading along with traditional religious norms on marriage and sex.

For the presidential campaigns, the data reflect a simple fact on the ground. Three-quarters of unaffiliated voters voted for President Barack Obama in 2008. Today the unaffiliated break like this: 65 per cent for Obama, 27 per cent for Republican challenger Mitt Romney.

Longtime GOP political strategist and pollster Ed Goeas said the challenge for Republicans in reaching unaffiliated people is, well, that they're unaffiliated. Unattached to religious institutions, they're hard to find. "They may be reachable message-wise, but not tactically," he said.

But what does the political platform of this mammoth group of voters look like?

The nones are strongly liberal on social issues, including abortion and same-sex marriage, but no different from the public overall and the religiously affiliated on their preference for a smaller government providing fewer services.

If they have an issue, it's that they don't believe religion and politics should mix. Only a third of them say it matters if the president is a believer. Three-quarters of the affiliated think it matters.

This divide, says religion and politics expert John Green, defines our culture.

"I suspect for these reasons that simmering cultural conflict for the last 30 or 40 years is likely to continue," said Green, who advised Pew on the study.

This chasm isn't news to religious or political leaders. Some political observers think one of the reasons Obama and Romney have both spoken minimally and in general terms about their faiths is that they haven't wanted to alienate unaffiliated voters.

And many rising evangelical leaders have pushed hard to uncouple their faith from the GOP, from the Rev. Mark Batterson, who runs an evangelical megachurch on Capitol Hill popular with congressional staffers of both parties, to Focus on the Family's new president, Jim Daly, who has said making Christianity less strident is his key mandate.

Lorna Stuart, 74, of Newport News, Va., describes herself as having "no particular religion" and says she votes Democratic because she is strongly in favor of abortion rights. She likes the fact that she doesn't often hear Democratic candidates talking about religion.

The retired Army analyst grew up in an active mainline Protestant family in Massachusetts. She went to youth groups and Sunday school and sang in the choir. She raised her children in the Methodist Church but said that at any time during her adult life, she would have told a pollster she didn't identify with a particular label.

She liked the social structure of the church and the idea of giving her children "something to rebel against," but she feels traditional religion is too focused on rules and sin and "things that really don't apply to God," she said in an interview Monday.

For the past 13 years Stuart says she has been in a weekly meditation and study group made up of people who have "fallen away" from some faiths and others who are still active.

"We are much more than churches give us credit for," she said of people outside major denominations. "I mean as people. We are spiritual beings on a human journey."

The beliefs of the unaffiliated aren't easy to characterize, as the Pew poll shows. The nones are far less likely to attend worship services or to say religion is important in their lives. But 68 per cent say they believe in God or a universal spirit, one-fifth say they pray every day and five per cent report attending weekly services of some kind.

As American religion is in full churn, experts often debate whether the country will go the way of Europe, with a more institutionalized secularism. But many note that religion has been a busy marketplace in America and continues to reinvent itself. Even if the structures and institutions and terms we know slip, Putnam said, it's unlikely that secularism will replace spirituality and faith in America.