Abstract: Empirical scholars of the United States Supreme Court, Jeffrey Segal and Harold Spaeth, have long contended that Supreme Court decisions are based primarily upon the ideological beliefs of the justices, and that ideology alone accounts for the bulk of choices made in civil liberties cases. However, this conclusion results from the misinterpretation of an ecological regression model. The researchers never modeled the votes of the justices; they only analyzed an index of grouped aggregates. When announcing conclusions, however, scholars equated variation in a voting index with the frequency distribution of binary observations that comprised it. As a result, model conclusions were exaggerated and disciplinary misinformation created. This work exposes and corrects this problem by re-estimating the relationship between justice ideology and votes with a multilevel approach that uses a logistic regression to directly examine the dependent variable prior to its manipulation into grouped data. The findings demonstrate that ideology models lose about two-thirds of the level of explanation researchers previously proclaimed. This new understanding supports a more limited critique of the role that ideology plays on the Court – one that has a long history in political science that predates the more value-dominant “attitudinal” framework.
- Working Paper: SSRN