A new report on global religious identity shows that while Christians and Muslims make up the two largest groups, those with no religious affiliation--including atheists and agnostics--are now the third-largest “religious” group in the world.

The study, released Tuesday (Dec. 18) by the Pew Forum on Religion & Public Life, found that more than eight in 10 (84 percent) of the world’s 7 billion people adheres to some form of religion. Christians make up the largest group, with 2.2 billion adherents, or 32 percent worldwide, followed by Muslims, with 1.6 billion adherents, or 23 percent worldwide.

Close behind are the “nones”--those who say they have no religious affiliation or say they do not believe in God--at 1. 1 billion, or 16 percent. That means that about the same number of people who identify as Catholics worldwide say they have no religion.

“One out of six people does not have a religious identity,” said Conrad Hackett, a primary researcher and demographer on the study. “But it is also striking that that overwhelming majority of the world does have some type of religious identity. So I think people will be surprised by either way of looking at it.”

While the number of the religiously unaffiliated is high, researchers are careful to point out that they are by no means homogeneous.

Surveys considered in this report show that 7 percent of unaffiliated Chinese report a belief in God or some other high power, while that number among the unaffiliated French is 30 percent, and among Americans it climbs to 68 percent. In China, 44 percent of unaffiliated adults say they have worshiped at a graveside or tomb in the past year.

The report covers 230 countries and is drawn from more than 2,500 censuses, surveys and population records accrued through 2010. It marks the first attempt to pin down a global religious landscape using such records, Hackett said.