Retesting Segal and Spaeth's Stare Decisis Model

Segal and Spaeth's (1996) innovative article constitutes the most ambitious attempt to date to empirically test whether stare decisis influences the votes of the justices on the United States Supreme Court. These two scholars inspect a 40% random sample of major, nonunanimous decisions of the Court in the 1953 through 1995 era as well as the progeny of these cases, i.e., orally argued, full opinion cases that applied "the holding of the majority or plurality opinion" of the major case. They test whether the dissenting justices in Case 1 (the major case) support the precedent of Case 1 in Case 2 (the progeny case) or vote the same way as they did in Case 1, i.e., vote their "preferences." Note two characteristics of their clever research design. First, they treat situations in which the justices' preferences (based on their vote in Case 1) indicates that they will vote one way and conformity to precedent indicates that they vote the other way. This is a productive way to proceed. For the best way of showing that a precedent is influential is to focus on the situation when conformity to precedent is in conflict with the justices' preferences. Second, Segal and Spaeth focus on major cases. They state that they chose these cases "because they are more likely to establish precedential guidelines for future cases and because they are more likely to actually generate progeny that we can analyze," (1996, 976). In addition, the rule of the law set forth in the major cases is likely to be sufficiently unambiguous and sufficiently dramatic that the justices in Case 2 will be forced to either uphold the precedent or refuse to do so. The justices cannot simply ignore the precedent.' Segal and Spaeth discover that justices vote their preferences 90.8%