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.