Estimating the Ideal Points of Organized Interests in Legal Policy Space

Abstract Scholars have been limited in the development and testing of theory regarding the incidence and impact of organized interest advocacy at the U.S. Supreme Court due to a critical measurement issue - the inability to properly locate these interests in the legal policy space in which the Court operates. We treat the positions articulated by organized interests in their amicus curiae briefs as “votes” in Court cases, allowing us to use an IRT model to estimate the locations of both the 600 most active organized interests and the justices in the same legal policy space. The resulting ideal point estimates yield substantive implications (e.g., the distribution of organized interest ideal points is slightly to the left of the justices) and lend themselves to a number of future applications to important questions involving judicial politics in the United States.