Measuring legislators’ ideological position in large chambers using pairwise-comparisons

Our understanding of politics often relies on the ideological placement of political actors—ranging from scaling legislative roll-call voting in the United States to text-based classifications of political parties in Europe. A particularly thorny problem remains estimating individual positions in legislatures with strong partisan discipline. We improve upon recently developed measurement strategies and propose a novel approach for estimating legislators’ ideological positions: an expert survey in which respondents compare pairs of representatives on a left-right dimension. The innovation of our approach lies in the combination of four particular features. First, we rely on political youth leaders who are insightful and easy to recruit. Second, the rating task does not involve numeric scaling and consists of simple pairwise comparisons. Third, we efficiently and automatically detect informative comparisons to reduce the cost and length of the survey without compromising our estimates. Fourth, we use a Bayesian Davidson model with random effects to generate an ideological position for each legislator. As an empirical illustration, we estimate the placement of the 709 members of the 19th German Bundestag. Several validity tests show that our model captures variation within and across political parties. Our estimates offer a thorough benchmark to validate alternative measurement strategies. The presented measurement strategy is flexible and easily extendable to diverse political settings because it can capture comparisons among political actors across time and space.