Soon media outlets will begin to tell the story about how influential evangelical Christians were in today’s presidential election. As today approached, it was unclear whether the traditional alliance between evangelical voters and the Republican Party would hold. Neither McCain nor Obama self-identify as evangelical, and neither candidate is perceived by evangelicals to be one of their own. Meanwhile, evangelicals may be broadening the range of issues that determine their vote beyond a candidate’s position on abortion and gay marriage, toward a wider agenda that includes issues such as poverty, AIDS, and climate change. Such a shift would reflect a cohort change among mainstream evangelical leaders, and perhaps the growing influence of the historically low-profile evangelical left.

The question used to identify evangelicals in today’s exit polls is “Would you describe yourself as a born-again or evangelical Christian?” Unfortunately, this is not a great survey question. One problem with this measure is that it produces estimates of the evangelical population considerably larger and different from estimates based on measures more commonly used by scholars. The measure originates with the Gallup Organization, which has been using it since 1986 to track the size of America’s evangelical population. It was introduced into presidential election exit polls in 2004. Despite Gallup’s reputation, the measure has several flaws. It is a double-barreled question that implies that “born-again” and “evangelical” are interchangeable labels, which may not be true for all respondents. It does not offer respondents alternate ways of expressing religious identity, which no doubt inflates estimates of the evangelical population. In this respect, a better question would be “Would you describe yourself as an evangelical Christian, another type of Christian, or a non-Christian?”

This measure produces inconsistent estimates about the proportion of the country that is evangelical. In 1998, Gallup estimates suggested that about half of the U.S. population was evangelical (47%). In 1986, they estimated the evangelical population at 31% of the country, and in 2007 Gallup estimated that 41% of the country was evangelical. Furthermore, the measure is used inconsistently. Sometimes the question is asked of all Americans, as is the case with Gallup surveys. In such surveys, Catholic, Orthodox, and Jewish respondents often identity as evangelical, although evangelical identity is usually classified by scholars as a Protestant category. In other surveys, only self-identified Protestants are asked whether they are evangelical. In discussions of voting behavior, analysis of this measure is often restricted to white respondents, who tend to vote differently than non-white evangelicals. I believe that tonight news agencies are only reporting on the exit poll results for white evangelicals.

Despite the above problems with the Gallup measure of evangelicalism, those it identifies as evangelical do tend to be distinct from the rest of the population in terms of their voting behavior and religious commitment. However, many social scientists prefer to measure evangelicals based upon their affiliation with a denomination in the Evangelical Protestant religious tradition, roughly captured by the membership of the National Association of Evangelicals. John Green of the Pew Center for Religion and Public Life, along with frequent co-authors James Guth, Lyman Kellstedt, and Corwin Smidt, for instance, use the denomination-based approach to make claims about evangelical behavior. Another way of measuring evangelicals is testing adherence to a series of belief measures, which is the approach used by University of Virginia sociologist James Davison Hunter in his studies of evangelicalism in the 1980s and in recent surveys from the Barna Research Group.

In the current issue of the Journal for the Scientific Study of Religion, D. Michael Lindsay and I discuss the consequences of using these various measures to gauge the evangelical population. A straightforward but important observation we make about these measures is that they often lead to conflicting claims about the size and characteristics of the evangelical population. Notre Dame sociologist Christian Smith and his colleagues produced an excellent study of evangelicals in 1998, which claimed that evangelicals were “embattled and thriving.” By design, Smith’s study defined evangelicals as those who described themselves as Protestant, regular churchgoers, and who chose “evangelical” from a list of Protestant identities. A footnote on the first page of his study notes, however, that these evangelicals constituted 7% of the country, a far cry from the Gallup estimate in that year that 47% of the country was evangelical.

As claims are made about the evangelical voter in the coming days, readers should consider how the evangelical population is measured in various surveys. Inevitably, the measure will change from survey to survey, likely leading to different interpretations of the evangelical vote. Readers should consider which people are included and excluded from the measures of evangelicalism in question. One of the most interesting aspects of the evangelical vote is likely to be the extent to which younger evangelical voters indicate that they voted for Obama, and the issues which they identify as motivating their vote.

[See also: Mapping the evangelical vote.—ed.]