Legislative Politics

Measuring ideological positions of legislators

Andrew Gelman Jul 23 '12

Anthony Fowler and Andrew Hall send along a new paper, “Conservative Vote Probabilities: An Easier Method for the Analysis of Roll Call Data”:

We propose a new roll-call scaling method based on OLS which is easier to imple- ment and understand than previous methods and also produces directly interpretable estimates. This measure, Conservative Vote Probability (CVP), indicates the probability that an individual legislator votes “conservatively” relative to the median legislator. CVP is a flexible non-parametric statistical technique that requires no complicated as- sumptions but still produces legislator scalings that correlate with previous roll call methods at extremely high levels. In this paper we introduce the methodology behind CVP and offer several substantive examples to demonstrate its efficacy as an easier, more accessible alternative to previous roll call methods.

The paper has lots of graphs! I don’t know what they think they’re doing, plotting correlations with bar graphs, but other than that the graphs are great.

Here’s my big question. Fowler and Hall talk a lot about how their estimates are close to those obtained by more complicated approaches. But to me the key point of contention nowadays is not the relative positions of legislators, or the increasing gap between the parties—both of these things can indeed be estimated in any number of simple or complicated ways—but rather the debate about the absolute positions of the parties. Is it really true, as Poole and Rosenthal’s calculations seem to show, that Democrats in congress have pretty much remained in the same place, ideologically, while the Republican party has moved sharply to the right? My impression is that these shifts are different for economic, social, and foreign policy issues, but Fowler and Hall (and also Poole and Rosenthal) seem pretty committed to the basically one-dimensional model. I’d be curious to see if Fowler and Hall’s approach can address the issue of absolute ideological positions.