ABSTRACT
In this chapter, the authors look at policy change in American history, with policy measured by both the location of groups of legislators and the locations of winning roll call outcomes in the voting space. They look at changes in the mean positions of the major political parties in the three major party systems: the Federalist/Republican system; the Whig/Democratic; and the Republican/Democratic. The authors show that their estimates of legislator coordinates are very stable from Congress to Congress, with the correlations almost always exceeding 0.95. The preferences expressed in a legislature can change because individual legislators change their own preferences, as measured by their spatial position. The authors consider replacement in Congress, including a detailed analysis of replacement since Reconstruction. They investigate the polarization of preferences. The authors also show that, to whatever extent roll call voting can be captured by a spatial model, a low-dimensional model — say, a one-and-a-half-dimensional one — suffices.
