Friends of the Court: Examining the Influence of Amicus Curiae Participation

Amicus curiae participation is a staple of interest group activity in the U.S. Supreme Court. While a reasonably large body of scholarship has accumu-lated regarding the effectiveness of this method of participation, little atten-tion has been paid to examining the reasons why amicus participation might increase litigation success. In this article, I test two separate, but not mutually exclusive, theories as to why amicus briefs may be effective. The first, the affected groups hypothesis, suggests amicus briefs are influential because they signal to the Court how many groups and individuals will be potentially af-fected by the decision. The second, the information hypothesis, proposes that amicus briefs are effective because they provide the Court with added infor-mation that buttresses the arguments of the direct parties. When subjected to empirical verification, the results indicate that not only does amicus partic-ipation increase litigation success, but also that this influence may be best explained by the information hypothesis. Interest groups pursue their goals in a wide array of venues, including the courts. Indeed, solely within the realm of the U.S. Supreme Court, groups have numerous methods for participation, from setting up test cases to sponsoring cases that others bring to testifying at judicial confirmation hearings; some groups even hold vigils outside the marble pillars awaiting the Court’s final decisions on cases touching on group interests. However, the most common method of interest group involvement in the Supreme Court is th