Assessing the Influence of Amicus Curiae Briefs on the Roberts Court

Objectives Our objective is to assess the influence of amicus curiae briefs on judicial behavior on the U.S. Supreme Court. Our primary hypothesis is that amicus briefs have an impact on the justices across the ideological spectrum. Our secondary hypothesis is that this influence will be greater for justices nearer the ideological center. Methods Our analysis is confined to the Roberts Court (2005 through 2014 terms, inclusive). The unit of analysis is the justice‐vote in each of the 793 full‐opinion decisions during this 10‐term period; thus, our data set contains 7,135 observations. We employ logistic regression to test the impact of amicus filings on the ideological direction of the vote cast by each justice in each case. We control for the direction of the lower court decision, the ideological orientations of the justices, the presence of the federal government (or agency or official) as party, and the presence of the solicitor general as amicus curiae. Results We find statistical support for both the primary and secondary hypotheses. Amicus briefs appear to influence the justices across the ideological spectrum. The influence is somewhat greater among the more moderate justices, although the relationship between amicus influence and judicial moderation is a weak one. Conclusions Supreme Court justices appear to respond positively to the persuasive attempts of amici. This impact is most noticeable for the justices in the middle of the Court—those who tend to be most influential in steering the Court's decision making.