WASHINGTON (CNS) — A major study of the religious landscape of the United States shows a continuing decline in the number of people who consider themselves part of any religion, with the largest shift occurring among the “millennial” generation.

The Pew Research Center survey of 35,000 people, conducted in 2014, found that the percentage of Americans who identify themselves as Christians declined by 8 percentage points since the last religious landscape survey in 2007. The first data from the survey, released May 12, dealt primarily with religious affiliation. Future reports will address other parts of the survey, such as religious beliefs and practices.

The phenomena of people changing religions also has become more pronounced, the survey found, and said that is especially true for people who were raised Catholic.

“Nearly one-third of American adults (31.7 percent) say they were raised Catholic,” the report said. “Among that group, fully 41 percent no longer identify with Catholicism. This means that 12.9 percent of American adults are former Catholics, while just 2 percent of U.S. adults have converted to Catholicism from another religious tradition. No other religious group in the survey has such a lopsided ratio of losses to gains.”

The report said the number of people who define themselves as religiously unaffiliated changed from 16 percent in 2007 to 23 percent in 2014.

Among those, the 51 million Catholics represents a decrease of about 3 million, or from 24 percent of the population to 21 percent. The study noted that the figure might be somewhat explained by the statistical margin of error, and could be as little as a decline of 1 million people.

It also added that Catholics’ percentage share of the population has remained relatively stable over decades, in comparison to Protestants, who have steadily declined.

A quibble with Pew’s numbers on Catholics was posted by Mark Gray, who studies Catholics for the Center for Applied Research in the Apostolate at Georgetown University. Gray said Pew’s figures for Catholics don’t reflect what other polls by Gallup, Public Religion Research Institute and the General Social Survey have found. Those consistently find between 21 percent and 26 percent of the U.S. population is Catholic, Gray said in a post on CARA’s “1984” blog.

Catholics are represented strongly among immigrants, however, the survey said. About 15 percent of those surveyed were born outside the U.S., and two thirds of those are Christians, including 39 percent who are Catholic. About 10 percent of immigrants said they belong to a non-Christian faith, including Islam or Hinduism.

However, among millennials, the survey showed sharp differences in the percentage of people who say they’re Catholic, in comparison to older generations. In the three older generations the survey considered, 20-23 percent of adults said they are Catholics. Among millennials, the percentage was 16 percent. Pew counted as millennials those who were born between the early 1980s and the mid-1990s.

Pew also considered how the people who say they have no religious affiliation define their beliefs. Between the surveys in 2007 and 2014, the number of “unaffiliated” people who say they are atheist or agnostic grew from 25 percent to 31 percent. Those who said religion is unimportant their lives also increased slightly.

Religions are also becoming more ethnically and racially diverse, the survey said.

Minorities now account for 41 percent of Catholics, it found, up from 35 percent in 2007. Among evangelical Protestants the increase was 24 percent, up from 19 percent seven years earlier, and 14 percent for mainline Protestants, up from 9 percent in 2007.

Religious intermarriage was found to be more common. The survey said 39 percent of people who said they had married since 2010 are in religiously mixed marriages, compared to 19 percent of those who married before 1960.

Other findings of the survey:

* The state with the highest percentage of Catholics is Rhode Island, with 42 percent. Other states on the high end include: Massachusetts, New Jersey and New Mexico, each with 34 percent, and Connecticut, with 33 percent. These states each have 25 percent Catholics or more: California, Illinois, Louisiana, Nevada, New Hampshire, New York, North Dakota and Wisconsin.

On the low end, Mississippi has the fewest Catholics, at 4 percent, Utah has 5 percent and West Virginia has 6 percent. Each of these states has fewer than 10 percent Catholics: Alabama, Arkansas, Georgia, North Carolina and Oklahoma.

* The age group with the most Catholics remained the same in the seven years between studies, but the percentages shifted a bit. The largest number of Catholics are still in the 30-49 age range, but now that age group makes up 33 percent of Catholics, compared to 41 percent in 2007. Now 20 percent of Catholics are over 65, compared with 16 percent seven years ago. The number of 18- to 29-year-old Catholics is about the same, 17 percent; it was 18 percent in 2007. And the percentage between ages 50 and 60 increased to 29 percent, up from 24 percent.

* Race and ethnic composition among Catholics changed most significantly in the percentages of whites and Latinos. In 2007, 65 percent were white and 29 percent Latino. In 2014, 59 percent were white and 34 percent Latino. In 2007, 2 to 3 percent of Catholics were — and still are — Asian, black or “other/mixed.”

* A higher percentage of Catholics in 2014 were lower income. In 2007, 31 percent of Catholics earned less than $30,000 a year, and 30 percent earned between $50,000 and $99,999. In 2014, 36 percent of Catholics earned less than $30,000 and 26 percent earned between $50,000 and $99,999. The other income categories remained about the same, with 19 percent of Catholics earning more than $100,000 and a similar percentage earning between $30,000 and $49,999.

* Fewer Catholic adults are married. In 2007, 58 percent of Catholics said they were married; in 2014, 52 percent were married. Slightly more Catholics said they are divorced — 12 percent in 2014, up from 10 percent in 2007. The number of those never married was 21 percent, up from 17 percent.