Religious affiliation in the United States is at its lowest point since it began to be tracked in the 1930s, according to analysis of newly released survey data by researchers from the University of California, Berkeley, and Duke University. Last year, one in five Americans claimed they had no religious preference, more than double the number reported in 1990.

UC Berkeley sociologists Mike Hout and Claude Fischer , along with Mark Chaves of Duke University, analyzed data on religious attitudes as part of the General Social Survey, a highly cited biannual poll conducted by NORC, an independent research institute at the University of Chicago.

Results of the survey – which looked at numerous issues, including attitudes about gun ownership and how tax dollars should be spent, and is funded in part by the National Science Foundation – are being released now and in coming weeks.

On American attitudes toward religion, UC Berkeley researchers found that 20 percent of a nationally representative group reported no religious preference. That’s a jump from 1990 when all but 8 percent of Americans polled identified with an organized faith.

“This continues a trend of Americans disavowing a specific religious affiliation that has accelerated greatly since 1990,” said Hout, lead author of the study.

Hout and Fischer are authors of the General Social Survey study that in 2002 first identified a rise in the number of “unchurched.” They are careful to distinguish the survey category of “no religion,” which means individuals who are not part of an organized religion, from “atheists,” who do not believe in God and made up just 3 percent of those interviewed last year. Meanwhile, just 8 percent of those surveyed said they were raised with no religion.

Responses in the survey were to the question, “What is your religious preference? Is it Protestant, Catholic, Jewish, some other religion, or no religion?”

An analysis of the results suggests the following:

Liberals are far more likely to claim “no religion” (40 percent) than conservatives (9 percent)

Men are more likely than women to claim “no religion” (24 percent of men versus 16 percent of women).

More whites claimed “no religion” (21 percent) compared to African Americans (17 percent) and Mexican Americans (14 percent).

More than one-third of 18-to-24-year-olds claimed “no religion” compared to just 7 percent of those 75 and older.

Residents of the Midwestern and Southern states were least likely to claim “no religion” compared to respondents in the Western, Mountain and Northeastern states. But Midwesterners and Southerners are catching up, Hout said.

Educational differences among those claiming “no religion” are small compared to other demographic differences.

About one-third of Americans identify with a conservative Protestant denomination, one-quarter are Catholics (although 35 percent were raised Catholic) and 1.5 percent are Jewish.

The General Social Survey has been tracking major social and cultural trends in American society since 1972, when only 5 percent of those polled claimed no religion. Since 1990, an uptick in those identifying themselves as following no particular religion has progressed steadily with 18 percent identifying as such in 2010 and 20 percent in 2012.

For more information, visit the General Social Survey website or download the study