In interpreting the study, which shows a drop in church attendance, Bible reading, and priority in faith, research group founder George Barna warned that American Christians have become complacent.
The study in regards to those identified by Barna Group as born-again Christians showed that:
Attendance at weekend church services has declined among this group by seven per cent since 1991, falling from 66 per cent to 59 per cent.
The proportion of born-again adults who read the Bible during the week, not including when they are at a church event, has decreased by nine per cent since 1991. The weekly average is now at 62 per cent.
Volunteering at church during the week for those identified as born-again Christians has dropped from 41 per cent in 1991 to 29 per cent today.
The study also found that those who self-identify as Christians are 10 percentage points more likely to be unchurched than in 1991. The 31 per cent who fit this profile have not attended any church service during the past six months, excluding special services such as weddings or funerals, according to the study.
Barna Group clarifies the "born-again" category as comprised of people whose beliefs characterise them as born-again and not based on people calling themselves "born-again". This group is now at 41 per cent of all Americans, an increase of six per cent since 1991.
Even with the increase in born-again Christians over the last 20 years, what has not increased is the participation in their faith, Barna said in his analysis of the study.
"As the number of born-again adults has increased, the engagement in the Christian life seems to have waned – a common problem when a product, service, movement, or perspective gains massive numbers and velocity," Barna stated.
Barna called the areas that dipped substantially in the last 20 years, such as church attendance and Bible reading, "critical reflections."
"In the past decade, even the proportion of born-again adults who say their faith is vitally important to them has dipped substantially," he noted.
Barna concluded his analysis of the born-again Christian segment of the study by saying that such a spiritual condition reflects the "pursuit of cheap grace", described by theologian and martyr Dietrich Bonhoeffer.
Ministry leader coach Scott Couchenour, founder of Serving Strong based in Ohio, said he was not surprised about the results of the study or Barna's analysis.
"Someone is once quoted as saying Americans are truly the poorest on the earth when it comes to spiritual wealth," Couchenour told The Christian Post. "I think George is right. In America, we have just too stinkin' much to keep us at a dangerous level of comfort, we don't want to or don't see the need to surrender at this level."
Couchenour said the decline in Bible reading could be the result of a number of things.
"I believe it's because of the tremendous wealth of distractions at our fingertips these days," he said.
"We have a generation that is being raised on a steady diet of technology and are used to 140-character tweets and 160-character Facebook updates. I was talking with an author the other day who said most books are now no longer than 12 chapters or say 500 pages."
When asked about the overall trend of complacency that the study reveals, Couchenour commented, "Perhaps what we've done in making church a really cool place, this excellence in all we do kind of thinking, is that we've allowed the people in the pews to evolve into a coasting mode."
Couchenour, who also works for a company specialising in church building design, said he often sees churches putting a lot of effort into making sure they have the latest technology.
"The question I have to ask is are we putting too much emphasis on the 'wiz-bang' at the expense of the real meat of church life? After everything is said and done, it will always come down to the walk. And that walk must be with a few close friends who are doing real life with each other, holding one another accountable. Jesus modelled it with the 12 disciples," he said.
Barna Group (which includes its research division, the Barna Research Group) is a private, for-profit organisation. According to its website, "It conducts primary research, produces media resources pertaining to spiritual development, and facilitates the healthy spiritual growth of leaders, children, families and Christian ministries."
Methodology: The conclusions drawn from the data are based on the annual OmniPoll survey of 1,000 or more adults and conducted by the Barna Group each January. The 1991 survey included 1,005 adults randomly selected from across the United States. The 2011 survey included 1,621 randomly chosen adults. Barna Group has been conducting such research since 1984. However, it was not until 1991 that many of the core tracking questions were developed and then followed annually.