Why Is It So Hard to Count the Catholic Population?

Answers to your questions about the news.
March 20 2013 3:44 PM

One Catholic, Two Catholics, Three Catholics ...

Why can’t demographers agree about how many Catholics are in the United States?

Nuns from the 'Instituto Serve del Signore, E Della Vergine Di Matara,' (Servants of the Lord and the Virgin of Matara,) react to the black smoke.
Nuns react to the black smoke seen from the chimney in St. Peter's Square on March 12 at the Vatican.

Photo by Dan Kitwood/Getty Images

Vice President Biden attended the installation of Pope Francis at the Vatican on Tuesday, representing the tens of millions of Catholics living in the United States. Precise estimates of American Catholics vary from 57 million to 78 million. How do you count Catholics?

Surveys, sacraments, or church records. The total number of American Catholics depends largely on what you think it takes to be a Catholic, with the numbers dropping as the required level of commitment increases. It takes very little effort to self-identify as a Catholic, so the Pew Research Center’s survey sets the Catholic population high at 75 million. The Catholic Research Forum has more rigorous standards, defining Catholics as people who are baptized into the church and arrange for a Catholic funeral. By this measure, there are approximately 68 million American Catholics. Finally, some demographers count only people who register at a church or regularly attend Mass. The U.S. Religion Census: Religious Congregations & Membership Study, which asked local church leaders to estimate the number of people in their congregations, set the American Catholic population at just 59 million. Weak church attendance accounts for this discrepancy: Only 24 percent of self-reported American Catholics attend Mass weekly. (Another church-generated estimate, the Official Catholic Directory, estimates the national flock at 66.3 million, but critics worry that clerics inflate the numbers for this publication for PR reasons.) What do these numbers mean? There’s a population of approximately 19 million Americans who think they’re Catholic but who are unknown to their local priests.

None of these methods accurately captures the Vatican’s view of the Catholic population. Under church law, baptism makes you a Catholic, and you remain a Catholic until you’re excommunicated or formally repudiate the faith. Since more people unilaterally abandon Catholicism than join it without baptism, the Vatican’s census is typically even higher than the number of self-identified faithful. The official Statistical Yearbook of the Church counts a total of 1.196 billion Catholics worldwide, or 96 million more than Pew does, a difference of about 9 percent. Variances within individual countries can be far more extreme. The Vatican’s estimate for Brazil is 29 percent higher than Pew’s.

Advertisement

Estimating the size of other Christian groups isn’t quite as challenging because self-identification is all that matters for many of them. In the United States, most demographers accept census data in estimating the size of the Lutheran or Presbyterian population, for example (8.6 million and 4.7 million, respectively, according numbers from 2008). In certain countries, census figures are either unreliable or nonexistent, forcing researchers to rely on health surveys and other interview methods.

Catholics aren’t the only religious group that presents a challenge to demographers. While calculating the worldwide Muslim population is fairly straightforward, breaking that number into Sunni and Shiite populations is not. Few surveys make that distinction, and many Muslims refuse to self-identify in one of those groups. As a result, in their 2010 report “Mapping the Global Muslim Population,” Pew relied on local ethnographers to estimate the approximate breakdown of Sunni and Shiite in each country’s population. The method was so improvisational—at least by Pew’s standards—that they were unable to provide a margin of error.

Got a question about today’s news? Ask the Explainer.

Brian Palmer writes about science, medicine, and the environment for Slate and the Natural Resources Defense Council. Email him at explainerbrian@gmail.com. Follow him on Twitter.

TODAY IN SLATE

Foreigners

The World’s Politest Protesters

The Occupy Central demonstrators are courteous. That’s actually what makes them so dangerous.

The Religious Right Is Not Happy With Republicans  

The XX Factor
Oct. 1 2014 4:58 PM The Religious Right Is Not Happy With Republicans  

How Did the Royals Win Despite Bunting So Many Times? Bunting Is a Terrible Strategy.

Catacombs Where You Can Stroll Down Hallways Lined With Corpses

Homeland Is Good Again! For Now.

Crime

Operation Backbone

How White Boy Rick, a legendary Detroit cocaine dealer, helped the FBI uncover brazen police corruption.

Music

How Even an Old Hipster Can Age Gracefully

On their new albums, Leonard Cohen, Robert Plant, and Loudon Wainwright III show three ways.

The One Fact About Ebola That Should Calm You: It Spreads Slowly

Piper Kerman on Why She Dressed Like a Hitchcock Heroine for Her Prison Sentencing

  News & Politics
Foreigners
Oct. 1 2014 6:41 PM The World’s Politest Protesters The Occupy Central demonstrators are courteous. That’s actually what makes them so dangerous.
  Business
Moneybox
Oct. 1 2014 2:16 PM Wall Street Tackles Chat Services, Shies Away From Diversity Issues 
  Life
Outward
Oct. 1 2014 6:02 PM Facebook Relaxes Its “Real Name” Policy; Drag Queens Celebrate
  Double X
The XX Factor
Oct. 1 2014 5:11 PM Celebrity Feminist Identification Has Reached Peak Meaninglessness
  Slate Plus
Behind the Scenes
Oct. 1 2014 3:24 PM Revelry (and Business) at Mohonk Photos and highlights from Slate’s annual retreat.
  Arts
Brow Beat
Oct. 1 2014 6:39 PM Spoiler Special: Transparent
  Technology
Future Tense
Oct. 1 2014 6:59 PM EU’s Next Digital Commissioner Thinks Keeping Nude Celeb Photos in the Cloud Is “Stupid”
  Health & Science
Science
Oct. 1 2014 4:03 PM Does the Earth Really Have a “Hum”? Yes, but probably not the one you’re thinking.
  Sports
Sports Nut
Oct. 1 2014 5:19 PM Bunt-a-Palooza! How bad was the Kansas City Royals’ bunt-all-the-time strategy in the American League wild-card game?