The question of how Protestantism (including evangelicalism) is measured in social science research is of keen importance to those seeking to understand religion in American life. In this article, we compare and contrast two of the leading techniques for classifying Protestants. One of these approaches (the RELTRAD approach) categorizes respondents as evangelical Protestants, mainline Protestants, or black Protestants mainly on the basis of their denominational affiliation. By contrast, the self‐identification method utilizes information about a respondent's race and a yes/no question that asks respondents directly whether they consider themselves born‐again or evangelical Christians to create similar categories. We show that there is considerable overlap, though not perfect correlation, between the two approaches. Both methods produce similar estimates of the size of Protestant subgroups, and they paint similar religious and demographic portraits of the evangelical, mainline, and black Protestant communities. As a result, we argue that the self‐identification method can be an effective proxy for RELTRAD when RELTRAD is unavailable as a measurement option.

Some U.S. surveys measure many religious identities, including detailed Protestant affiliations. Researchers must decide how to aggregate these diverse identities. There are now a variety of options for aggregating religious groups into categories. Depending on the research question, it may be appropriate to use one of the existing options or to develop an aggregation strategy tailored to the project in question.

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