Conventional wisdom holds that amicus briefs provide the Supreme Court with information that is not otherwise supplied by litigants and that the Court finds this information useful. While several studies explore the information that amici contribute to the Court in certain notable cases, judicial scholars have no systematic knowledge regarding the nature of information furnished by amici or the Court's use of it in its opinions. We argue that amici curiae briefs are important because they reduce information problems at the Court by helping the justices anticipate the impact of their opinions. To test conventional wisdom, we examined all party briefs on the merits and amicus briefs filed in the 1992 term. We found that the conventional wisdom is largely inaccurate. First, amicus briefs often contribute unique arguments, but they also commonly reiterate their party's brief. Second, the Court's majority opinions are not more likely to use arguments from amicus briefs that offer new information. In fact, the Court is much less likely to adopt arguments from amicus briefs that exclusively add arguments not found in their party briefs, even after controlling for a variety of alternative explanations. The implication is that amici influence is not a function of the independent information they convey.
Nearly all past research on amici curiae implicitly, if not explicitly, argues that amicus briefs convey critical and reliable information to the Courtinformation that the Court's members find useful in making decisions (see Caldeira and Wright 1988; Epstein 1993: 659). Indeed, conventional wisdom suggests that courts often rely on factual information or analytical approaches offered by amici, but not otherwise advanced by the parties to the case. Judicial scholars frequently point to, among other cases, Mapp v. Ohio (1961) and Webster v. Reproductive Health Services (1989) to illustrate these tendencies. Some argue that the American Civil Liberties Union singlehandedly transformed Mapp, a case involving the possession of obscene materials, into the seminal ruling extending the exclusionary rule to states (Epstein and Walker 1995: 538; Ivers and O'Connor 1987: 163; McGuire and Palmer 1995). This was done, they argue, because the ACLU raised the exclusionary rule issue in its brief, while Mapp and Ohio both argued the case on obscenity grounds. Similarly, other scholars suggest that Chief Justice Rehnquist's opinion in Webster went beyond the appellant's arguments by adopting the technical and legal information advanced in the appellant's amici briefs undermining Roe v. Wade's trimester framework (Behuniak-Long 1991: 270).
In spite of these notable examples, judicial scholars have no systematic knowledge about the information amicus briefs provide the Court or the degree to which the justices use such arguments in their opinions. In looking at amici activity in specific cases or the activity of certain amici, several earlier studies find that amici sometimes supplement parties' arguments and that the Court occasionally uses such information (Behuniak-Long 1991; Epstein 1993; Ivers and O'Connor 1987). However, the absence of systematic samples precludes making general conclusions (see Epstein 1993: 694-99). We do not know, for example, to what extent amici reinforce the arguments provided by litigants, as opposed to bringing independent issues and ideas to the Court. Even if amici contribute unique information, we do not know to what extent the Court uses their arguments in its majority opinions. In other words, political scientists lack information on whether amici supply novel information and whether the Court incorporates their arguments in its opinions.
AMICUS BRIEFS AND INFORMATION
Judicial scholars commonly assert that amicus briefs provide novel information that the Court uses in its opinions. One commentator notes: "Courts often rely on the factual information, cases or analytical approaches provided only by an amicus" (Ennis 1984: 603). …