How many in mainline? Categories vary in surveys

http://www.christiancentury.org/article.lasso?id=7152

[The Christian Century] 1 June 2009--Americans who identify with mainline churches make up either 18 percent of the U.S. population or 13 percent, according to two large-scale surveys taken within recent years. Which is right?

Both are, say some researchers. The statistical variations typically depend on what questions are asked and how the mainline is defined.

Few doubt that the graying of members, low birth rates and various controversies have contributed to the diminishing numbers of mainline Protestants found in the United Methodist Church, the Evan gelical Luth eran Church in America, the Pres byterian Church (U.S.A.), the Epis copal Church, the American Baptist Churches and the United Church of Christ.

But has the slippage become precipitous, threatening to reduce mainline Protestants ever closer to remnant status? "A generic form of evangelicalism is emerging as the normative form of non-Catholic Christianity in the United States," said Mark Silk, who helped design the 2008 American Religious Identification Survey (ARIS).

That survey, which polled more than 54,000 adults, reported in March that the number of mainline Christians had slipped to 12.9 percent of adult Americans—down from 17.2 percent in 2001 and 18.7 percent in 1990—as evangelical numbers grew.

By contrast, the Pew Forum's U.S. Religious Landscape Study, after polling 35,000 adults in 2007, reported last year that 18.1 percent of adults said they were affiliated with "mainline Protestant" churches.

Asked about this 5 percent difference, senior fellow John C. Green of the Pew Forum on Religion & Public Life said, "It isn't that our numbers are more right than [ARIS's] numbers . . . but how one conceptualizes the group."