  Spatial voting models of legislators' preferences are used in political
science to test theories about their voting behavior. These models posit that
legislators' ideologies as well as the ideologies reflected in votes for and
against a bill or measure exist as points in some low dimensional space, and
that legislators vote for positions that are close to their own ideologies.
Bayesian spatial voting models have been developed to test sharp hypotheses
about whether a legislator's revealed ideal point differs for two distinct sets
of bills. This project extends such a model to identify covariates that explain
whether legislators exhibit such differences in ideal points. We use our method
to examine voting behavior on procedural versus final passage votes in the U.S.
house of representatives for the 93rd through 113th congresses. The analysis
provides evidence that legislators in the minority party as well as legislators
with a moderate constituency are more likely to have different ideal points for
procedural versus final passage votes.
