KIM LAWTON, guest anchor: The Pew Forum on Religion & Public Life released a comprehensive new survey this week (February 25) looking at America's religious landscape. The study confirmed a widespread fluidity among faith traditions, with nearly half of all Americans either switching out of the denomination they grew up in or leaving religion all together. Catholics saw the biggest number of defections, although those numbers were largely offset by a big influx of Catholic immigrants. Sixteen percent of Americans were unaffiliated with any particular faith. That was the fasting growing group in the survey.

Joining me to help interpret some of this is Nancy Ammerman, who teaches sociology of religion at Boston University. Nancy, I know these numbers document a lot of trends you've been studying for years. What does all this religious switching mean?

Dr. NANCY AMMERMAN (Professor, Sociology of Religion, Boston University): Well, Americans have been of a mind to choose their own religious tradition really almost from the very beginning. In some sense, we see that with the Pilgrims coming to these shores to choose their own way of being religious, and that's simply, in some way, part of our Protestant heritage. But it really picks up steam in the post-World War II period, as more and more people are moving away from the communities where they grow up. They're going off to college, they're meeting new people, they are mixing things up in ways that we perhaps hadn't seen before. And that has simply accelerated with the generation of the baby boomers who have now raised their kids, and we're seeing, I think, in many ways the fruits of those very longstanding religious trends.

LAWTON: And other religious traditions have been influenced by the Protestants, so we saw this large number of Catholics leaving their church. How significant is that?

Dr. AMMERMAN: Well, I think we would not have seen that 50 or 75 years ago, and we didn't see it in those earlier days. Partly that's a result of the kinds of changes that took place in the church itself in the 1960s, with the Second Vatican Council and more emphasis on Catholics owning the tradition for themselves and being able to make more choices within the tradition, and for many people then choosing to leave the tradition, choosing to marry outside the Catholic faith. So I think we've seen in some ways the result of that change in the Church. But I think we also can't discount the kinds of things that have been happening more recently, with the scandals that have taken place in the church, with the parish closings that have accelerated, Catholic schools being closed, people's sense of the church itself leaving them at the same time that they're feeling more free to leave the church.

LAWTON: And this study found a rapidly growing number of people who call themselves unaffiliated. Does this mean that America is becoming less religious?

Dr. AMMERMAN: Well, it's important to note that in the study itself that about half of those people who are unaffiliated are nevertheless religious in some sense. We're still not at all a nation of unbelievers. But we are a nation that has a growing segment of people who don't find any of the currently organized religious traditions to their liking.

LAWTON: And what does this say about the future of religion in America?

Dr. AMMERMAN: Well, I think it says that we will continue to be a country where people will change over the course of a lifetime, where our changing family structures will also have a big impact on how religion interweaves with our lives over a lifetime. But I don't see us, by any means, leaving religion behind as an important factor in our overall culture.

LAWTON: And very briefly, what message should some religious leaders take from this?

Dr. AMMERMAN: Well, perhaps they should pay special attention to those questions about family and about how people are making decisions in their marriages as their children come along, with complicated step-families and all the kinds of changes people are experiencing -- that churches and synagogues and mosques are going to need to take those things into account in helping people to make choices about where they affiliate and how.

LAWTON: OK. Nancy Ammerman, thank you.