Measuring Party Identification in Public Opinion Surveys of Americans

How should we measure "pure" or "true" independents? For years, the respective item required a respondent to volunteer that answer. Recent surveys have moved toward presenting it explicitly. Those that do produce estimates of pure independents that are much larger than in past surveys. We present evidence of this phenomenon across multiple surveys and ask: Are self-administered surveys overcounting independents, or are traditional live-interviewer surveys undercounting independents? We answer that question by comparing live-interview and self-administered samples from the 2012 and 2016 American National Election Studies, by undertaking tests to rule out mode effects (including an experiment), and by seeing which question wording correlates more strongly with measures of latent ideology, vote choice, and ratings of the parties. Our findings suggest that surveys that include an explicit response option, allowing Americans to self-identify easily as "(pure) independent," offer a more precise measurement of the concept of party identification. This has implications for the study of independents, as well as for discussions about polarization and party-system dealignment.