Nuannuan Xiang and Yuki Shiraito. 2024. “A Dynamic Dirichlet Process Mixture Model for the Partisan Realignment of Civil Rights Issues in the U.S. House of Representatives” Unpublished manuscript.

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Abstract

The positions of the two major parties in the United States on civil rights issues reversed in the 20th century. The conventional wisdom views the reversal as a structural break in the 1960s led by party elites, whereas recent work argues that the change occurred gradually from the 1930s driven by local activists within both parties. To address this debate, we develop a nonparametric Bayesian model that incorporates the hidden Markov model into the Dirichlet process mixture model. In analyzing rank-and-file legislators’ behavior, we model the emergence and disappearance of their latent voting blocks as a gradual process rather than a one-time structural change, thereby identifying both steady and sudden changes of voting coalitions. Our analysis shows that, in addition to gradual changes of party positions beginning in the 1930s, Democrats and Republicans in southern States formed a voting coalition from 1950s.