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.”

The next largest groups, the report finds, are Hindus (1 billion people, or 15 percent), Buddhists (500 million people, or 7 percent) and Jews (14 million people, or 0.2 percent). More than 400 million people — 6 percent — practice folk traditions from African, Chinese, Native American or Australian aboriginal cultures.