There have been significant shifts in the electoral coalitions assembled by the Democratic and Republican parties in recent decades, with implications for how these parties govern when in office. To better understand these changes, we estimate the latent ideological preferences of American voters over 40 years, and examine the changing association between issue preferences and partisan choice for subgroups of voters. We do this using the combined files for the American National Election Study surveys from the 1970s to the 2000s. We fit a single ordinal, multi-dimensional item response theory (IRT) model to these data, estimating respondents’ ideological locations in two dimensions across this period.   We identify movement in citizen ideological locations with constraints on the item parameters.  We use estimates of ideological location to understand shifts in party support and to examine how different demographic groups are cross-pressured.

Shaun Ratcliff is a lecturer in political science at the US Studies Centre at the University of Sydney. His research focuses on the use of quantitative methods and survey data to understand public opinion, political behaviour and the role of parties in both the United States and Australia. In particular he is interested in how these have changed over time. Shaun has a background working in politics and government relations, and has consulted for federal election campaigns.