Friends of the Court: Examining the Influence of Amicus Curiae Participation in U.S. Supreme Court Litigation

Amicus curiae participation is a staple of interest group activity in the U.S. Supreme Court. While a reasonably large body of scholarship has accumulated regarding the effectiveness of this method of participation, little attention 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 affected by the decision. The second, the information hypothesis, proposes that amicus briefs are effective because they provide the Court with added information that buttresses the arguments of the direct parties. When subjected to empirical verification, the results indicate that not only does amicus participation increase litigation success, but also that this influence may be best explained by the information hypothesis.