Associated Press: A wide-ranging study on American religious life found that the Roman Catholic population has been shifting out of the Northeast to the Southwest, the percentage of Christians in the nation has declined and more people say they have no religion at all.

Fifteen percent of respondents said they had no religion, an increase from 14.2 percent in 2001 and 8.2 percent in 1990, according to the American Religious Identification Survey.

Northern New England surpassed the Pacific Northwest as the least religious region, with Vermont reporting the highest share of those claiming no religion, at 34 percent. Still, the study found that the numbers of Americans with no religion rose in every state.

"No other religious bloc has kept such a pace in every state," the study's authors said.

In the Northeast, self-identified Catholics made up 36 percent of adults last year, down from 43 percent in 1990. At the same time, however, Catholics grew to about one-third of the adult population in California and Texas, and one-quarter of Floridians, largely due to Latino immigration, according to the research.

Nationally, Catholics remain the largest religious group, with 57 million people saying they belong to the church. The tradition gained 11 million followers since 1990, but its share of the population fell by about a percentage point to 25 percent.

Christians who aren't Catholic also are a declining segment of the country.

In 2008, Christians comprised 76 percent of U.S. adults, compared to about 77 percent in 2001 and about 86 percent in 1990. Researchers said the dwindling ranks of mainline Protestants, including Methodists, Lutherans and Episcopalians, largely explains the shift. Over the last seven years, mainline Protestants dropped from just over 17 percent to 12.9 percent of the population.

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