Do the Justices Vote Like Policy Makers? Evidence from Scaling the Supreme Court with Interest Groups

Research in judicial politics often assumes that Supreme Court justices vote on the basis of one-dimensional policy preferences. This article challenges this assumption using multidimensional scaling in two dimensions to compare the justices’ votes with positions taken by interest groups in Supreme Court cases. Focusing on two active groups, the National Association of Criminal Defense Lawyers and the US Chamber of Commerce, the article demonstrates that the voting alignments of the justices deviate substantially from the policy dimensions identified by the interest groups. Although the scaling approach cannot determine whether the divergence is due to countervailing policy influences or disagreements about legal methodology, a qualitative examination of the cases suggests some of both.

These findings cast doubt on the notion that the Court operates in a one-dimensional policy space and suggest the need for more nuanced models of judicial motivation.