Almost three-quarters of Catholics and Protestants who are now unaffiliated with a religion said they had "just gradually drifted away" from their faith. And more than three-quarters of Catholics and half of Protestants currently unassociated with a faith said that over time, they stopped believing in their religion's teachings.

Pew Forum senior fellow John C. Green said that result surprised researchers, who had expected policy disputes or disillusionment over internal scandals -- such as the clergy sex-abuse crisis in the Catholic Church -- to play more of a role in people's decision to leave a faith.

Among former Catholics who became Protestants, one in five cited the sex-abuse scandal as one of several reasons why they had left the church. But only a small percentage -- 2 to 3 percent -- cited it as the lone reason. "It suggests that what leads people to leave their faith is that, somehow for some reason, it isn't meeting their needs . . . religion becomes less plausible to the person," Green said.

The study is a follow-up to a Pew report on religious identity released last year that was one of the largest polls of its kind. Researchers recontacted 2,800 of the 35,000 adults they previously interviewed for that study for in-depth interviews on how many times, and why, they had changed religious affiliations.

Researchers interviewed non-Christians but focused their analysis on Christians, which provided them with large enough groups to permit close scrutiny, said Pew research fellow Gregory A. Smith. Researchers discovered that the "churn" among the faithful and formerly faithful was higher than first estimated.

In this second round of interviews, they found that some people who currently belong to the religion in which they were brought up had tried a different faith at some point, causing researchers to raise their estimate of the people who have changed faith at some point in their lives from 44 percent to 56 percent. They also found that up to one-third of people who have left their childhood faith have jumped around among three or more other faiths.

The results are a "big indictment" of organized religion, said Michael Lindsay, assistant professor of sociology at Rice University and author of a book on evangelical leaders.

"There is a huge, wide-open back door at most churches. Churches around the country may be able to attract people, but they can't keep them."

At the same time, the large and growing number of people who report having no religious affiliation are surprisingly open to religion, researchers said. Unlike the popular perception that many have embraced secularism, a significant percentage appeared simply to have put their religiosity on pause -- having worshiped as part of at least one faith already, about three in 10 said they have just not yet found the right religion.

"We tend to think that when people leave [religion] they leave," said Stephen Prothero, chairman of the religion department at Boston University. "But a lot of these unaffiliated are unaffiliated for now. . . . It's not a one-way street. It's not like after you've left a religious affiliation, you can't get back in."

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