The Pew Research Center's Forum on Religion & Public Life has released a new study that looks at the rise of people in the U.S. who do not identify with any religion. Audie Cornish speaks with Gregory Smith, Pew Forum senior researcher and co-author of the study, for more on that growing segment of the population.

AUDIE CORNISH, HOST: As we watch polls in the presidential race bounce around, here's a poll that shows a consistent shift in American society. More people than ever before consider themselves religiously unaffiliated. That's a key finding in a survey out today from the Pew Research Center's Forum on Religion and Public Life. And coauthor Gregory Smith joins us to talk about it. Welcome, Gregory.