Decomposing Public Opinion Variation into Ideology, Idiosyncrasy and Instability

We propose a method for decomposing variation in the issue preferences that US citizens express on surveys into three sources of variability that correspond to major threads in public opinion research. We find that, averaging across a set of high profile US political issues, a single ideological dimension accounts for about ¹⁄₇ of opinion variation, individuals’ idiosyncratic preferences account for about ³⁄₇, and response instability for the remaining ³⁄₇. These shares vary substantially across issue types and the average share attributable to ideology doubles when a second ideological dimension is permitted. We also find that (unidimensional) ideology accounts for almost twice as much response variation (and response instability is substantially lower) among respondents with high, rather than low, political knowledge. Our estimation strategy is based on an ordinal probit model with random effects, and is applicable to other data sets that include repeated measurements of ordinal issue position data.