Think former parishioners have left the pews because of sex scandals? Or because they no longer believe in God?
While some have departed for those reasons, the vast majority of former Catholics and former Protestants who are now unaffiliated with any faith have "just gradually drifted away," according to the Pew Forum on Religion & Public Life.
The new analysis, called "Faith in Flux: Changes in Religious Affiliation in the U.S.," found that 71 percent of both former Catholics and former Protestants said their decision to leave happened over time, unprompted by any one-time event. The report was released April 27.
"For many people, religious change is not a decision that's reached at a particular point in time after careful deliberation of the pros and cons," said Greg Smith, research fellow at the Washington-based Pew Forum. "There's really a ... gradual element to it."
The new study is a follow-up to a wide-ranging Pew study of 35,000 Americans last year. The earlier study found, among other things, that 44 percent of Americans had moved away from the faith of their childhood, and one in 10 Americans are former Catholics. The new study tried to tease out the reasons behind those changes.
When former Catholics were asked specifically about clergy sex-abuse scandals, just 27 percent of those who are now unaffiliated, and 21 percent of Protestant converts, said it was an important reason for leaving the church. When asked an open-ended question, less than 3 percent of former Catholics cited pedophilia scandals as the main reason they left the church.
"The poster child of former Catholics is a disaffected teenager," said Catholic researcher Mark Gray, not a parade of angry parishioners storming out over sex abuse or teachings with which they disagree. "This is about youth coming of age and not feeling connected to their faith."
Catholic leaders have tried to respond, said Gray, of Georgetown University's Center for Applied Research in the Apostolate, with initiatives like "Theology on Tap" sessions for 20-somethings at bars and the Vatican's YouTube channel.
For people who changed affiliations within Protestantism, the key reasons for departing their childhood religion are finding a religion they liked better (58 percent) or unmet spiritual needs (51 percent).
Michael Lindsay, a sociologist of religion at Rice University, said the findings show that people are making individualized decisions about their faith and are not driven by feelings of betrayal over a pastor's scandal, for example, or how their kids were treated in the church nursery.
"Both among Catholics and Protestants ... it's more about sort of personal decision-making as opposed to discontent with somebody else," he said.
Less than half of people who are now unaffiliated said that the reason for their withdrawal from faith was because they "just do not believe in God" or most religious teachings. Forty-two percent of former Catholics felt this way, as did 39 percent of former Protestants.
An even smaller percentage of former Catholics and Protestants -- 32 percent -- said "modern science proves religion is superstition" and about a quarter of them cited that as an important reason for their disaffiliation.
"The sort of presumed conflict between religion and science doesn't seem to be driving people away from the faith," Lindsay said.
Overall, the reasons for changing faiths can range from disagreement with specific church tenets to seeking a new way to worship to marrying outside a childhood religion.
"I was struck in these data by the degree to which the reasons that people give for having changed religions are every bit as diverse as the religious landscape itself," said Smith. "You cannot point to a single reason."
For those who are now unaffiliated, though, three-quarters saw religious people as hypocritical, judgmental and insincere; slightly more than 50 percent cited that image as an important reason why they are no longer affiliated with a faith.
But one in three of the unaffiliated appear open to return to a faith in the future, saying they "just have not yet found the right religion for them."
Among ex-Catholics, 65 percent who are now unaffiliated said they "stopped believing" in church teaching," along with 50 percent of those who became Protestants. Asked about the Catholic Church's specific teachings on abortion and homosexuality, 56 percent of former Catholics who are now unaffiliated said it was an important reason for their departure, compared to 23 percent of former Catholics who are now Protestant.
The follow-up study to last year's U.S. Religious Landscape Survey involved follow-up interviews with more than 2,800 people. The margin of error varied, from plus or minus 6.5 percentage points for those raised Catholic and now unaffiliated, to plus or minus 10 percentage points for those who were born and remain unaffiliated.
Because of the small sample size, researchers were unable to probe deeply into several groups of converts: the 3 percent of Protestants who became Catholics; or the 4 percent of Protestants and 3 percent of Catholics who embraced another faith.
Experts said the findings -- which also indicated that many people change faith more than once in their lifetimes -- may give hope, or at least guidance, to religious leaders, who often don't learn the specific reasons why worshippers leave their faith.
"It suggests there is a market out there," said Lindsay. "If you lose somebody, it doesn't necessarily mean you lose them for the rest of your career. If we're thinking of it like a religious marketplace, you might lose the customer for a year, but you might bring them back with a new product line."