Objectifying the Measurement of Voter Ideology with Expert Data

Many surveys require respondents to place themselves on a left-right ideology scale. However, non-experts may not understand the scale or their "objective" position. Furthermore, a uni-dimensional approach may not suffice to describe ideology coherently. We thus develop a novel way to measure voter ideology: Combining expert and voter survey data, we use classification models to infer how experts would place voters based on their policy stances on three axes: general left-right, economic left-right and libertarian-authoritarian. We validate our approach by finding i) a strong connection between policies and ideology using data-driven approaches, ii) a strong predictive power of our models in cross-validation exercises, and iii) that "objective" ideology as predicted by our models significantly explains the vote choice in simple spatial voting models even after accounting for the subjective ideological distance between voters and parties as perceived by the voters. Our results shed new light on debates around mass polarization.