There have been a number of breathless headlines about the recent Pew Research report, especially around the idea that Muslims are growing faster than Christians. Although, even in the Pew report, Christians continue to be the largest religious segment in the world.
That Muslims are growing faster, currently, is not actually all that new.
That Muslims are growing faster, currently, is not actually all that new. It has been known for a long while and the Status of Global Christianity 2025 report reaffirmed this in January. In that January report, for the period 2020-2025, Islam was growing at 1.6% p.a., while Christianity was growing at 0.98%. But, we need to keep one thing in perspective: in the Global South, where Christianity is most in competition with Islam, Christianity is growing at 1.6%, matching Islam’s growth rate. In the Global North, where Christianity is competing with agnosticism, it’s declining by -0.41%, while the nonreligious are globally growing at 0.19%.
The global number of Christians in 2020 was 2.5 billion.
When I read the Pew report, what left me scratching my head, was when you do the math, the Center for the Study of Global Christianity's (CSGC) January report estimates the global number of Christians in 2020 at 2.5 billion—while Pew’s number totals to 2.27 billion. In other words, Pew’s Christian population in 2020 is nearly a quarter of a billion people (approximate to the population of the United States) smaller than the World Christian Database. It is reasonable to wonder why?
Unfortunately, the two are not directly comparable in a region by region stack-up; largely because Pew divides its numbers into Sub-Saharan Africa and Middle East/North Africa, and combines Asia and the Pacific, while CSGC follows the UN convention with Europe, North America, Africa, Asia, Latin America and Oceania. But, we can combine them:
But there is still a difference. Why? Digging into the Pew report, the first thing that stood out to me was on page 20 where is states, ”This Pew Research Study is the first to report on observed patterns of switching into and out of religious groups at the global level.” I’m guessing they actually mean this is the first Pew Report to do so; the World Christian Encyclopedia and the Operation World international prayer guide have both been doing this for decades.
Still, the analysis is apparently accounting for both natural growth and conversion (what Pew calls "religious switching"). Let’s move past the next 140 pages or so of the report, and jump straight to page 162, where "Data sources by country or territory" begins.
All the Pew sources are census data and public opinion polls.
Looking through this, one thing stands out immediately: all the Pew sources are census data and public opinion polls. In other words, Pew’s analysis is looking solely at what is called "professing" data, and ignoring the "affiliated" data—the actual membership in churches as reported by the denominations.
That’s challenging. First of all, while page 20 made a big deal about "religious switching," digging into the data sources shows 79 countries with "data unavailable" for switching. Granted, many of these are smaller countries (Fiji, etc)—but they also include a number of so-called "10/40 Window" countries, and countries where well-known movements to Christ are under way (such as Sierra Leone for example).
Where data on religious switching is available to Pew, it again comes from surveys, polls, and census work—not, seemingly, from any denominational data.
Moving on to page 180 and the religious composition table, we find most of the countries of the world are broken out by 2010 and 2020 total population and religious percentages. I did a quick spot-check and found their estimates for China’s Christian percentage: 2.3% in 2010, and 1.8% in 2020. The source for this is the Chinese General Social Survey.
CSGC puts the total number of believers in China at over 100 million.
In their 2011 report, Pew discussed the challenges with using this number—but it’s the number they're using anyway. CSGC puts the total number of believers in China at over 100 million; and others estimate it at over 10%.
I believe 2% is far too low an estimate. Further, to say that Christianity in China has declined from 2010 to 2020 is something that should be challenged. Most of the analyses I’ve seen suggests the growth has tapered off, but not that the Church is declining in number there.
The percentage of Christians in India was also estimated at 2.3% in 2010 and 2.2% in 2020. This, I believe, is a clear under-estimate. The number is based on the census, which is known to have under-counted Christians for a number of reasons.
Operation World estimated Christians in India in the last edition at 5.8%. Operation World also estimated Indian Christianity growing at over 3% per year, and I know of plenty of movements growing in most of the non-Christian states in India. There is no measure other than the official census that would estimate Christianity in India is in decline. All other evidence is to the contrary.
Another problematic estimate is to say that Christianity in Iran has declined from 0.2% to 0.1%: this is to go from 150,000 to 87,000, or cut in half in terms of percentages.
While I don’t think the Pew report is deceptive, neither do I think it is accurate.
Given the constraints that the Pew report seems to have put on itself in terms of methodology and data sourcing, they’ve done a decent job. But while I don’t think the Pew report is deceptive, neither do I think it is accurate.
At the global level, it carries some of the same conclusions as the Status of Global Mission and the World Christian Database, but its specifics seem very shaky. Where the two most populous countries in the world (China and India) have their own percentage of Christian figures colored by figures from government censuses and government-influenced think-tanks, I fear the rest of the report is also susceptible to a variety of similar, less-visible biases.
I highly recommend we stick with the data produced by CSGC each year, drawn out of the global analyses from the World Christian Database.
Originally published in Justin Long's Weekly Roundup Premium Edition. Republished with permission. CDI editorial changes made to the original content when first published, with an aim to strengthen comparison between Pew and Global Christianity data sets, have been removed, with apologies given to the author.
Justin Long has been involved in missions since 1990, beginning with the Association of International Mission Services and the World Christian Encyclopedia. He led the development of strategicnetwork.org in 2000 and supported research efforts in Southeast Asia from 2004 to 2008. As the Director of Global Research at Beyond since 2009, he documents movements to Christ and serves the 24:14 Network while editing the Weekly Roundup for mission leaders worldwide.
