With churches largely mapping out their local mission around what they identify to be an "unchurched" population, a research firm set out to paint a clearer picture of who unchurched Americans really are.

"There's a whole industry seeking to help clergy reach the unchurched, with seminars, books, videos, training centers, and consultants," Ron Sellers, president of Ellison Research, noted. "However, many people don't really have a basic notion even of just what it means to be 'unchurched'. There's often an assumption that people either do attend worship services, or they don't.

"But what we find in this study is that up to one out of every five Americans is attending worship services at least occasionally during the year, even though they are not regularly involved. That has huge implications for local congregations who are trying to attract new people," Sellers added.

Traditionally, people who attend worship service at least once a month and on a regular basis have been considered "churched" whilst those who do not attend frequently enough have often been labelled "unchurched", according to the Phoenix-based research firm.

A new study, released Monday by Ellison Research, broke down the American population into a more detailed picture of religious service attendance.

Results showed that only 63 per cent of "churched" Americans actually attend worship services once a week or more; 12 per cent of the "churched" attend three times a month; 16 per cent attend twice a month; and 9 per cent go to service once a month.

Among "unchurched" Americans, not all stay away from worship services, the research firm reports. Findings revealed that 18 per cent of the "unchurched" say they visit services occasionally, just not regularly. In addition, 22 per cent of the "unchurched" attend on special occasions such as Christmas and Easter.

Sixty per cent of the "unchurched" do not attend worship services at all, the Ellison study found.

The study showed what attendance at religious services actually looks like: 11 per cent attend more than once a week; 22 per cent attend once a week; 14 per cent two to three times a month; 5 per cent attend once a month; 9 per cent attend occasionally, but not on a regular basis; and 10 per cent attend only on religious holidays.

Overall, 29 per cent of Americans never attend worship services.

The study further linked worship attendance to several factors, including family history of attendance and parental religious involvement.

Those least likely to attend service regularly are Americans who are not born again and whose parents did not attend service.

With both parents attending religious services at least occasionally, there is a 62 per cent chance that their children are now regularly attending services as an adult.

Also, if an adult attended worship services regularly at some point before the age of 18, there is a 55 per cent chance that person is currently attending once a month or more. The odds decrease to 21 per cent for a person who never attended prior to age 18.

With millions of Americans likely to attend services, the Ellison Research head wonders if churches are paying attention to the newcomers.

"We estimate that up to 43 million adults who do not regularly attend worship services will visit a church or place of worship at some point during the year, to say nothing of children and teens who visit with their family or on their own," Sellers said. "Are those congregations and clergy members ready for them?"

The study was conducted on a sample of 1,007 adults.