Free Expression, In-Group Bias, and the Court's Conservatives: A Critique of the Epstein-Parker-Segal Study

83 Pages Posted: 22 Sep 2014 Last revised: 22 Apr 2015

See all articles by Todd E. Pettys

Todd E. Pettys

University of Iowa - College of Law

Date Written: January 2015


In a recent, widely publicized study, a prestigious team of political scientists concluded that there is strong evidence of ideological in-group bias among the Supreme Court’s members in First Amendment free-expression cases, with the current four most conservative justices being the Roberts Court’s worst offenders. Beneath the surface of the authors’ conclusions, however, one finds a surprisingly sizable combination of coding errors, superficial case readings, and questionable judgments about litigants’ ideological affiliations. Many of those problems likely flow either from shortcomings that reportedly afflict the Supreme Court Database (the data set that nearly always provides the starting point for empirical studies of the Court) or from a failure to take seriously the importance of attending to cases’ details. Whatever the difficulties’ sources, the study’s uniform indictment of the Court’s current conservatives is manifestly flawed. More broadly, the study and its largely uncritical public reception -- as well as the authors' initial response to this critique of their work -- offer important cautionary lessons not only for those who study in-group bias, but also for all who conduct or rely upon empirical analyses of the justices’ ideological voting patterns.

Keywords: speech, expression, first amendment, in-group, ingroup, bias, Supreme Court database, Epstein, Segal, Parker

JEL Classification: K10, K19, K30, K39, K40, K49

Suggested Citation

Pettys, Todd E., Free Expression, In-Group Bias, and the Court's Conservatives: A Critique of the Epstein-Parker-Segal Study (January 2015). 63 Buffalo Law Review 1 (2015), U Iowa Legal Studies Research Paper No. 14-25, Available at SSRN: or

Todd E. Pettys (Contact Author)

University of Iowa - College of Law ( email )

Melrose and Byington
Iowa City, IA 52242
United States
319-335-6814 (Phone)
319-335-9098 (Fax)

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