From the article at Barna.org:

In Churchless, their first collaborative effort, Barna Group founder and former president, George Barna, and current Barna president and owner, David Kinnaman, take a look at the rising population of adults who do not attend church.

Based on two decades of Barna Group interviews with thousands of churchless men and women, the book outlines a profile of the unchurched and the cultural context that has led to the trend away from church.

“It’s critical to recognize these trends have a huge impact on how our churches and faith organizations work,” says David Kinnaman in a joint interview with George Barna. “It is harder today—based on this data—to go out and say ‘invite your friends to church.’ So recognizing the context in which these trends play out is very important for church leaders, and for us as researchers.”

According to the Churchless data, in the 1990s, 30% of the American population was unchurched. Today, two decades later, that percentage has risen to more than four in 10 Americans (43%).

“If we want to turn that trend around,” says George Barna, “we’ve got to understand what these people are thinking, what they’re doing, why they are making these particular choices, what we could do to actually serve them better, to understand them, to love them, to do everything we can to help them get closer to God. . . . Armed with this kind of information, it’s a lot more likely that you’ll come up with a strategy that enables you to have positive impact on the lives of such people.”

Kinnaman agrees, “Jesus asks us to be faithful wherever we are, in whatever context we are. So good information helps us to learn how to be faithful.”

George Barna & David Kinnaman on the Rise of the Churchless – Barna Group.