Senator Obama seems to be ahead of Senator McCain among most faith groups. Among Catholics, he leads 39 percent to 29 percent. But he has slipped since June.What's interesting to me about polling, although I know nothing about it, is the formulation of categories. Here is what the article says about categorizing evangelicals. Anybody know if they have as complicated an approach to categorizing Catholics?Understanding EvangelicalsOne of the most frequently reported on groups of voters is evangelicals. Most media polls use a simplistic approach to defining evangelicals, asking survey respondents if they consider themselves to be evangelical. Barna Group surveys, on the other hand, ask a series of nine questions about a persons religious beliefs in order to determine if they are an evangelical. The differences between the two approaches are staggering. Using the common approach of allowing people to self-identify as evangelicals, 40% of adults classify themselves as such. Among them, 83% are likely to vote in November. Among the self-reported evangelicals who are likely to vote, John McCain holds a narrow 39% to 37% lead over Sen. Obama. Nearly one-quarter of this segment (23%) is still undecided about who they will vote for. Using the Barna approach of studying peoples core religious beliefs produces a very different outcome. Just 8% of the adult population qualifies as evangelical based on their answers to the nine belief questions. Among that segment, a significantly higher proportion (90%) is likely to vote in November, and Sen. McCain holds a huge lead (61%-17%) over the Democratic nominee. Overall, just 14% of this group remains undecided regarding their candidate of choice.