Not only do 1 in 5 Americans now admit they have no religious affiliation, most of the rest overstate their church attendance.
This is not news to parish priests who know that many of the people on the books of their parish only attend periodically if at all.
NPR's Steve Inskeep and Science Correspondent Shankar Vedantam talk about this phenomenon.
VEDANTAM: Well, leaders of several religious denominations for many years in the United States have said if 45 percent of Americans are attending church every Sunday, the pews should be packed. And in many churches, in many denominations...
INSKEEP: They're not.
VEDANTAM: ...that's simply not the case. Now, I spoke with a sociologist who studies church attendance. His name is Philip Brenner. He's at the University of Massachusetts in Boston. And he told me that he suspected that when you ask people whether they attend church, they actually end up answering a somewhat different question. Here he is.
PHILIP BRENNER: The question that asks how often do you attend becomes a question like: Are the sort of person who attends? The respondent hears the question how often do you attend and interprets the question to be: Are you the sort of person who attends?
INSKEEP: What you're really finding out here is I think I'm the sort of person who should attend church and I don't want to admit otherwise, so I might tell you I go, whether I do or not.
VEDANTAM: Exactly. So the question is about your behavior. What is it you're doing? The answer might be about people's identity. Am I the kind of person who attends church?
INSKEEP: OK. So, you can't necessarily rely on people's own testimony as to whether they attend church. So is there is a better way to measure this?
VEDANTAM: Yeah. So Brenner has been playing with this idea called the Time Diary Method, and he's been following studies that have used this Time Diary Method. And let me tell you what that is.
So, rather than tell people you're asking about their church attendance, what you do is you march people through their week and have them describe to you exactly what they're doing at any given moment. So you say: What were you doing at four o'clock in the morning on Sunday? And most people will say: I was asleep. And then you ask them: What did you do next? Who were you with? Where did you go?
And when you march people through the week in this manner, it turns out only about 24 percent of Americans actually report attending religious services in the past week. And Brenner told me there's two things that's very interesting about this. What this suggests is that in actual religious practice, Americans might not be that different from people in Western Europe when it comes to what they do, but they might be very different for people in Western Europe when it comes to reporting what they do.
BRENNER: Americans significantly over-report their church attendance, and have consistently done that since the 1970s. But we don't see substantive over-reporting in Western Europe.
INSKEEP: So, basically, what we're finding out is that Europeans are more comfortable saying they don't show up on Sunday.