Old-school preachers used to call them "backsliders," those folks who were raised in the pews but then fled. Sociologists and church-growth professionals eventually pinned more bookish labels on these people, calling them the "unchurched" or describing them as "spiritual, but not religious."

Pollsters at the Pew Forum on Religion & Public Life and similar think tanks are now using a more neutral term to describe a key trend in various religious traditions, talking about a sharp increase in the percentage of Americans who are "religiously unaffiliated."

That's certainly an awkward, non-snappy label that's hard to use in headlines. It's so much easier to call them the "Nones."

Anyone who cares about the role of religion in public life had to pay attention to last year's "Nones of the Rise" study by the Pew researchers, especially the jarring fact that 20 percent of U.S. adults -- including 32 percent under the age of 30 -- embrace that "religiously unaffiliated" label. The question some experts are asking now is whether Americans have simply changed how they describe their beliefs, rather than making radical changes at the level of faith and practice.

While there has certainly been a rise in the number of "religiously unaffiliated" people, when researchers "dig down inside the numbers they will find that there hasn't been that much change in the practice of religion in America," said Frank Newport, editor-in-chief at Gallup, in a recent telephone interview.

"What's happening is that people who weren't practicing their faith and have never really practiced a faith are now, for some reason, much more likely to be honest about that fact," he said. "People used to say that didn't go to church, but they would still call themselves 'Baptists,' or 'Catholics' or whatever. ...

"It's that lukewarm, vague sense of religious identity that is fading. We're seeing a lot more truth in the reporting, right now."

It's especially important to note that young people who were raised in intensely religious, traditional homes are much more likely to continue practicing their faith, or to become active in a similar faith, according to a new Focus on the Family report (.pdf), built on the Pew Research Center numbers and the most recent General Social Survey from the National Science Foundation.

In the Millennial Generation -- young people born in the 1980s and '90s -- only 11 percent of those who now call themselves "religiously unaffiliated" said they were raised in a home in which a faith tradition was enthusiastically lived and taught.

The Focus on the Family study noted: "This is not a crisis of faith, per se, but of parenting. ... Young adults cannot keep what they were never given."

So what has changed? Experts at the Gallup Poll have been asking similar questions about religious identity and practice for decades, noted Newport, and it's clear that in the past it was much harder for Americans to face a pollster and muster up the courage to openly reject religion -- period.

"I found the survey in the '50s where it was zero percent 'none.' How's that? I mean literally, it rounded down to zero," said Newport, drawing laughter during a recent Pew Forum event. "So it's amazing that back when the Gallup interviewer came a-calling -- and it was in person in the '50s -- literally it looks like almost every single respondent chose a religious identification other than 'none.' "

Now, it's becoming clear that -- perhaps following the cultural earthquakes of the 1960s -- many Americans have stopped pretending they are linked to faith traditions that they have no interest in practicing. These "unreligious" Americans, Newport told the Pew gathering, are not really changing how they live their lives, they "are just changing the way that they label themselves."

Meanwhile, it may be time for researchers to pay renewed attention to what is happening among the Americans on the other end of the spectrum -- those who remain committed to faith-centered ways of life, said Newport, in the telephone interview.

"It's possible that if you really claim a religion today, then it's much more likely that your religious identity is pure, that you're making sacrifices to practice your faith because it really means something to you," he said. "Maybe it's significant that so many people are willing to stand up and say that they still believe."