Who is Ideological? Measuring Ideological Consistency in the American Public

Political constraint and issue consistency are key variables in the study of public opinion, but the existing literature contains many parallel but contradictory accounts of the sources and predictors of ideological constraint. Some posit that constraint is essentially a function of a person's partisan commitment, others suggest it is rooted in participation in politics, while others see a wide range of correlates summarized as "sophistication." Still others deny that constraint exists in the mass public altogether. Contrary to these accounts, we argue that issue consistency exists within the American public and is best predicted by political knowledge, which should be thought of as separate from those other predictors. In fact, after accounting for political knowledge, other variables like partisanship, participation, and demographic variables have little independent relationship to ideological constraint. The data show that political knowledge is about as strong a predictor of issue consistency as is one's self-placed ideology - a widely used proxy for constraint. These results help us understand how citizens think about politics and which groups of people most closely resemble elites in the structure of their opinions. Our findings show that previously hypothesized predictors of constraint - particularly partisanship and participation - are mainly related to ideological constraint through a person's level of political knowledge.