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.