A new study of the 34 million American adults who do not identify with any particular religious group finds that they now largely mirror the wider population in other aspects. However, the group tends to be young, male, politically independent and of Irish ancestry.

The number of “Nones” grew greatly in the 1990s. In 1990 they made up 8.2 percent of the population and grew to 14.2 percent by 2001. In 2008 they made up 15 percent.

The Nones were the only group to have increased in every state and region of the country during the past 18 years, according to a study released by Trinity College Hartford today.

The researchers’ category of Nones include those who are irreligious, unreligious, the anti-religious, and anti-clerical. About 59 percent is agnostic or deist, while a small minority is atheist. About 27 percent profess belief in a personal God. Some participate occasionally in religious rituals, while others say they never would.

Nones increasingly mirror the wider population’s divisions of ethnicity, income, and education levels. About 19 percent of American men are Nones, though only 12 percent of women are. Women are less likely to be atheists and to take hard skeptical positions. About 33 percent claim Irish ancestry, while 28 percent now live in southern states.

About half came from a family where both parents identified with the same religion, while 17 percent came from a family where neither parent did so. Only 32 percent of current Nones said they had no religion at age 12, meaning that about two-thirds were raised with a religion.

Around 24 percent of Nones identified as Catholic at age 12, compared to 26 percent of the general population, the report says. However, former Catholics make up 35 percent of new Nones, the largest single group.

About 22 percent of adults under the age of 30 self-identify as Nones. Professor Ryan Cragun said that if current trends continue, in two decades the Nones could account for about 25 percent of the U.S. population.

The study, titled “American Nones: The Profile of the No Religion Population,” was conducted by Trinity College Professors Barry Kosmin and Ariela Keysar. They were assisted by Professor Ryan Cragun of the University of Tampa and Juhem Navarro-Rivera of the University of Connecticut.

Researchers studied the results of the 2008 American Religious Identification Survey (ARIS) which questioned 54,461 adults in English or Spanish between February and November 2008. The survey claimed a margin of error of plus or minus 0.3 percent for the entire population.

“The secularity of the American public is undoubtedly increasing but the pace varies considerably between how individuals belong, believe and behave,” said Kosmin. “The overall trend is being pushed by men and the young but slowed down by women’s greater religiosity.”

Navarro-Rivera discussed their political leanings, saying “Politically, older Nones were often libertarian Republicans but the younger generation of Nones, born after 1973, has associated the Republican Party with the Religious Right and, as a result, split between the Democrats and the Independents.”