Oftentimes a party will argue before a state supreme court (1) that the court should undertake an independent analysis of its state constitution and recognize broader civil liberties protections than provided under the analogous provision(s) of the Federal Constitution. The party may support its argument with decisions of other state supreme courts expanding rights under their state constitutions. In opposition, the court may be presented with decisions of still other state courts interpreting their state constitutions consistent with United States Supreme Court interpretation of the Federal Constitution. While there are other sources of authority to which the court may turn to resolve state constitutional questions, including its own previous decisions, state constitutional language, and state constitutional history, (2) the court may ultimately look to out-of-state decisions for guidance. (3)
This is an example of what Professor Alan Tarr identifies as state court interpretation of state constitutions within a "universe of constitutions." (4) Although the United States Supreme Court generally has chosen not to look to state court interpretation of state provisions when interpreting the Federal Constitution, state supreme courts oftentimes have looked within this pool of cases when interpreting their constitutions. (5) Indeed, New Jersey Supreme Court Justice Stewart G. Pollock urged state courts in a 1985 article to engage in this "horizontal federalism" and communicate decisions affecting fundamental rights for other state courts to consider when interpreting their state protections. (6)
The body of scholarship--much of it generated by political scientists--seeking to explain why a state supreme court chooses to expand rights under the state constitution has not, to date, addressed the influence of decisions rendered by other state supreme courts. While scholars cannot read the minds of the justices to determine how sister-state pronouncements may have impacted the resolution of their state constitutional issues, the judicial opinions generated in these cases do serve as written accounts of their decisions, and within these opinions, justices will usually include citations to other cases both from the same court and, oftentimes, from other courts. (7) These citations may provide some insight into the extent to which state courts communicate with each other over the meaning of state constitutional provisions and engage in horizontal federalism.
This study investigates the level of horizontal federalism in state civil liberties interpretation through a citation analysis of state constitutional decisions. Focusing solely on the portions of the majority opinions interpreting the scope of the protections afforded under the state constitutions, support for horizontal federalism is found, as the courts included in the study cited decisions from other state courts in over one-third of their decisions. (8) The level of citation to other state court decisions was higher in those decisions in which the state court afforded citizens broader rights under the state constitution than provided under analogous provisions of the Federal Constitution. These results provide initial empirical support for horizontal federalism, but, as more fully discussed below, it may be that future levels of out-of-state citation will fall, as states increasingly build up their own precedent from which state constitutional decisions may be constructed.
Part I of this article briefly addresses how existing empirical studies of decision-making under the new judicial federalism have failed to incorporate the influence of horizontal federalism, and how a citation pattern study can provide some preliminary evidence of inter-court communication to be considered in future investigations. (9) Part II of this article sets out the methodology used to collect and analyze the data to study citation patterns, (10) and the results are presented in Part III. …