Philadelphia Fed, Report: The Changing Polarization of Party Ideologies

“U.S. congressional roll-call voting records show that as polarization of the two parties along
the economic dimension changes, polarization along the social/cultural dimension tends to
change in the opposite direction. A model of party competition within a two-dimensional
ideology space is developed in which party platforms are determined by voters who compose
the party. It is shown that if distribution of voter preferences is radially symmetric, polar-
ization of party ideologies along the two dimensions are inversely related, as observed. The
model gives a remarkably good quantitative account of the historically observed movements
in polarization along the two dimensions …”