By the Numbers: Who Are Catholics in America?
A Catholic priest leading a service.
Credit: Diego Cervo | Shutterstock.com

This week, when Pope Francis visits the United States for the first time, he will see a Catholic population that mirrors the country overall.

Catholics make up the single largest religious group in the United States, with 22 percent of U.S. residents identifying as Catholic and nearly half of Americans saying they have at least some connection to Catholicism, according to new research.

This huge umbrella category encompasses Americans of almost every ethnicity, creed, socioeconomic status and political stripe. Given the huge number of people who identify as Catholic in this country, an overarching picture of their politics and beliefs is hard to pinpoint, said Daniel Cox, the director of researcher at the Public Religion Research Institute (PRRI), a nonprofit organization that researches the intersection of religion and public life.

"The Catholic vote is the most important vote, and also, there is no Catholic vote," Cox said. [Infographic: The Catholics of the United States]

Strong identity

Of those Americans who identify as Catholic, about four in 10 say they go to Mass at least once a week, while about 16 percent say they rarely or never attend Mass, according to a Pew Research Center survey conducted in June.

About one in 10 people say they are culturally Catholic even though they may attend different religious services or not believe in God at all. Many of these cultural Catholics were raised in the church and consider it part of their heritage through ancestry, family traditions or some other aspect of culture, the survey found.

By and large, the Catholic faith inspires a sense of strong loyalty: 70 percent of those who identify their current religion as Catholic say they could never imagine leaving their faith, the Pew survey found.

However, almost half of the people who are raised in the church do leave it at some point in their lives, with a fifth of those becoming "reverts," meaning they returned to Catholicism, the Pew survey found. In total, about 15 percent of Americans consider themselves former Catholics, according to an August 2015 telephone survey conducted by PRRI.

It's not clear why Catholics abandon their religious affiliation, but disagreement over social issues could be a factor, Cox said.

"I think Catholics are actually leaving the church over the issue of same-sex marriage and treatment of gay and lesbian people," Cox told Live Science. "The fact that the Church was so active in promoting opposition to same-sex marriage at a time when the public — in particular young people — were voicing strong support, I think it hurt the Church and it is continuing to be weighing them down in trying to get millennials really involved."

The picture of Catholics in America has also changed over the decades. For instance, 79 percent of Catholics over age 65 are white non-Hispanics. But only 40 percent of those Catholics between ages 18 and 29 are white, with almost half of this group identifying as Hispanic, the PRRI survey found.

Sexuality, family and social teaching

Though Catholics may feel a strong connection to their faith, many disagree with church teaching when it comes to sex, marriage and family life. For instance, only 17 percent of Catholics view contraception as a sin. By contrast, the Catholic Church teaches that sex has two primary functions: procreation and the unity of a couple, and to deliberately sever the connection between sex and procreation is intrinsically immoral.

Other Catholic no-no's, such as living together before marriage and remarrying after divorce, are also accepted by most Catholics, the survey found. About a quarter of Catholics have been divorced, and one in 10 have remarried. The Catholic Church views remarriages as living in adultery unless the church has annulled the previous marriage, meaning it was invalid in the first place.

People often reconcile their views with church teachings by placing less weight on doctrine that they disagree with, Cox said.

"People are both Catholics, but they're also mothers and fathers. They might be police officers and lawyers," Cox told Live Science. "You see that in a lot of issues — personal experience or personal necessity may supersede church teaching."

In addition, Catholics are evenly split on whether the church should accept same-sex marriages, the Pew survey found. Because the church views procreation as one of the inherent purposes of marriage, unions between couples who can never naturally conceive as a couple are not considered marriage by the Catholic Church. "Homosexual acts" are considered "intrinsically disordered," according to the Catechism of the Catholic Church. About 4 percent of people who consider themselves Catholic also identify as gay, lesbian or bisexual, according to a 2014 survey conducted by the Pew Research Center. [Same-Sex Marriage: 6 Effects of Supreme Court Decision]

In PRRI's research poll, a majority of Catholics said they supported same-sex marriage: 58 percent either favored or strongly favored the institution, compared with 54 percent of the general public.

Catholics also tend to mirror the general population on the issue of abortion, with about 49 percent saying that abortion should be legal in all or most cases, compared with 45 percent of the general public who thought the same, the PRRI survey found. The Church views abortion as the deliberate taking of an innocent human life, which is a mortal sin that can lead to ex-communication.

Social justice and environment

In general, Catholics tend to agree with the Pope and the church's teachings on social justice and care for the poor. About 60 percent of Catholics say working to help the poor is an essential part of Catholicism, the Pew survey found. [Infographic: The World's Catholic Population]

Climate change, however, doesn't inspire the same fervor in Catholics. Only 23 percent consider it a sin to use energy when it's not needed (presumably things like leaving the lights no when not needed or driving gas-guzzling cars), and only 29 percent consider working to address climate change a central mission of the church, according to the Pew survey. (The survey was conducted prior to the Pope's climate change encyclical, "Laudato Si," which states that climate change is a global problem with grave implications, and that many scientific studies suggest human-caused greenhouse gas emissions are the primary culprit in warming, so it's possible Catholic opinion has shifted since then, the study authors acknowledge.)

Catholics also tend to be slightly less supportive of the death penalty than the general public; 54 percent of Catholics prefer life in prison without parole as the appropriate punishment for murder, with just 40 percent preferring the death penalty. In contrast, about 44 percent of the general population view the death penalty as the preferred punishment for murderers, with 48 percent preferring life in prison, according to a 2014 American Values Survey conducted by PRRI. The church considers the death penalty justified only if it is the only possible way to defend human lives against an unjust aggressor. [Mistaken Identity? 10 Contested Death Penalty Cases]

Big divides on the small scale

Though Catholics tend to mirror the country as a whole, drill down deeper and there are big differences among certain populations of the faithful.

"For some Catholics, what's essential to Catholic teaching is helping the poor and the underserved and really being generous and trying to make a difference through social acts and acts of charity," Cox said. "For others, it might be the ethos of [being] pro-life: the idea that every life is sacred."

For instance, people who attend Mass regularly tend to hew closer to the Church's teachings on social issues. Only 34 percent of Catholics who attend Mass weekly say that same-sex couples raising children is as good as any other arrangement, according to the Pew research. And nearly six in 10 Catholics who attend Mass at least weekly say homosexual behavior is a sin, compared with slightly more than a third who attend less regularly, according to the Pew survey.

And when it comes to climate change, 61 percent of Hispanics say they believe humans have caused the Earth's warming, compared with just 40 percent of white Catholics. Hispanics are also much more likely to oppose the death penalty; just 29 percent prefer the death penalty, compared with 45 percent of white Catholics who see death as the preferred punishment for convicted murderers, the 2014 PRRI survey found.

Follow Tia Ghose on Twitter and Google+. Follow Live Science @livescience, Facebook & Google+. Original article on Live Science.