Measures of political ideology and beliefs are not appropriate for measuring ideologies in people’s heads because they primarily measure stable traits
Ideology and political beliefs are individual-level phenomena that are intended to describe the political thoughts of a person. However, the modal study of the structure of political ideologies and beliefs uses cross-sectional survey data to estimate what is central to the belief system or the dimensionality of the belief system. Cross-sectional data are ill-suited to the task of studying individual-level phenomena because they contain an unobservable mixture of within-person and between-person variation. In this project, we use longitudinal datasets from the Netherlands and the United States, spanning between 6 months and 10 years, to we ask whether the modal study helps us understand the ideologies in people’s heads? First, using Bayesian STARTS models (Lüdtke, Robitzsch, & Wagner, 2018), we find that variability in measures of ideology and political beliefs is primarily due to stable between-person differences, with relatively smaller amounts variation due to within-person change. Second, we estimate between-person, within-person, and cross-sectional correlations between all items in our study and find that between-person correlations are substantially different from within-person correlations. Between-person correlations are larger and in some cases differ in their direction from within-person correlations. Cross-sectional correlations are most similar to between-person correlations, suggesting that the modal study may help describe divisions between people but is ill-suited to tell us about the structure of individual’s ideologies and political beliefs. New methods are necessary for a complete understanding of political attitudes that can focus on both between- and within-person processes.