Explaining plurality decisions

Many of the Supreme Court's most important decisions, such as those involving executive power and the constitutionality of abortion regulations, are decided by plurality decision. Plurality opinions result when five or more Justices agree on the result in a particular case but no single rationale or opinion garners five votes. Many Justices, including William Rehnquist and Ruth Bader Ginsburg, have addressed the problems created by plurality opinions, such as interpretive difficulties in determining the Court's holding, but few scholars have addressed plurality decisions other than in passing. In the first empirical analysis examining the occurrence of plurality decisions, the authors present two statistical models to examine a variety of ideological, collegial, contextual, and legal factors to determine which factors are most likely to lead to plurality decisions. The case-level model draws on data for every Supreme Court case decided between the 1953 and 2006 Terms of the Supreme Court. The results of the study are illuminating. For example, a case is more likely to result in a plurality decision if it involves an issue of constitutional interpretation with respect to a civil liberties issue and lower court conflict did not influence the decision to grant certiorari. Importantly, the empirical results of the case-level model indicate that ideological forces bear no relationship to the occurrence of plurality decisions, and strategic considerations only appear in cases which have a minimum winning coalition. In addition, the authors estimate an individual-Justice model that measures which factors are most likely to lead to votes by Justices to concur in the judgment, which is the key ingredient for a plurality opinion. The opinion author's ideological distance from and prior lack of cooperation with a particular Justice both play a large role in whether the Justice joins the majority and separately concurs or votes to concur in the judgment. Unlike the case-level model, these results show that the Justices' ideological orientations influence their decisions to concur in the judgment. In addition, many of the same factors found influential in the case-level model are also found to influence Justices' decisions to concur in the judgment. Given the importance of plurality decisions to understanding the Supreme Court, this Article provides the basis for further normative evaluations of whether plurality decisions harm the development of the law and how such decisions should be interpreted by lower courts.