Historically, the percentage of Americans who said they had no religious affiliation (pollsters refer to this group as the "nones") has been very small -- hovering between 5 percent and 10 percent. However, Putnam says the percentage of "nones" has now skyrocketed to between 30 percent and 40 percent among younger Americans.
Putnam calls this a "stunning development." He gave reporters a first glimpse of his data Tuesday at a conference on religion organized by the Pew Forum on Faith in Public Life.
The research will be included in a forthcoming book, called "American Grace."