When political scientists and pollsters discuss faith and politics, one of their biggest challenges is separating the true believers from those who merely say they are believers.

It's kind of like distinguishing between "football fans" and "FOOTBALL FANS," said John C. Green of the University of Akron, who for decades has been a trailblazer in studies of politics, pulpits and pews.

"Lots of people say they're football fans and they like to watch games on television," said Green. "Then there are the people who buy jerseys and get decked out in their team colors. They never miss a home game and everything that goes with that. You can just look at them and know that they're really FOOTBALL FANS."

In terms of faith and politics, oceans of ink have been spilled describing the beliefs and goals of evangelical Protestants, Catholics and members of other religious groups, he said. The problem is that there are "self-identified" evangelicals and then there are truly faithful evangelical Christians. There are plenty of people who tell pollsters they attend worship services every week and that their faith shapes their lives. Then there are those who truly walk that talk.

"All religious communities have lots of highly committed people, and all religious communities have their share of marginal members whose faith isn't all that active," said Green. For pollsters, the challenge is asking questions that help draw lines between "self-identified believers and those who are truly active" in their faith groups, he added.

The American Bible Society, in its "State of the Bible" surveys, has tried to document ways in which beliefs about the Bible, and personal interactions with scripture, separate "practicing Christians" from "self-identified Christians." This matters, in part, because religious groups containing a high percentage of committed believers usually maintain their members, or even make converts, while other groups struggle to survive.

The most recent ABS survey (.pdf here) was completed last January, with data collected from 3,354 online interviews with adults in all 50 states and the District of Columbia. The American Bible Society began studying these kinds of issues as early as 1812.

In this survey, a "practicing Christians" was defined as someone who "identifies as a Christian, attends a religious service at least once a month" and states that "faith is very important" in his or her life. Thus, said the report, practicing the faith affected their lives "in a transformative way." Meanwhile, "self-identified Christians" were those who "simply say they believe." According to this study, in America:

* Evangelical churches include 58% "practicing Christians" and 42% who are "self-identified."

* Historically Black churches -- evangelical, Pentecostal and "mainline" combined -- are 31% "practicing" and 69% "self-identified" Christians.

* America's more liberal "mainline" churches -- many of which still contain significant numbers of evangelicals -- include 28% "practicing" Christians and 72% "self-identified."

* U.S. Catholic parishes are made up of 22% "practicing" and 78% "self-identified" Christians.

This survey found that 67% of the "practicing Christians" were what the researchers called "Scripture engaged" believers -- those who were most likely to "interact with the Bible regularly" while seeking to let biblical principles "influence their relationships with God and others." The religious groups with the highest numbers for weekly Bible reading were evangelicals (93%), historically black Protestants (87%) and mainline Protestants (80%).

"Practicing Christians" were highly likely, the study noted, to say that they believe the Bible is the "actual word of God and should be taken literally, word for word" or the "inspired word of God and has no errors although some verses are meant to be symbolic rather than literal." Those less active in religious groups tended to say the Bible was "not inspired by God but tells how the writers of the Bible understood the ways and principles of God" or that it's "just another book of teachings written by people that contains stories and advice."

Defining "religious commitment" in strictly biblical terms is a "very Protestant way to look at these issues," said Green, and may miss the importance of worship and sacraments in ancient, liturgical Christian traditions. However, it's true that commitment to scriptures and doctrines is almost always linked to the practice of a faith.

"It's pretty logical," he added. "If you really believe something, then you tend to show up in a pew."