In a democracy, constituencies hold their representatives accountable by mapping performance onto reelection. However, the democratic input into the federal judiciary is limited. Justices of the U.S. Supreme Court, for instance, are commonly perceived as largely unaffected by the ebb and flow of politics. Still, in a thought-provoking and masterfully written volume, Collins challenges this perception of judicial decisionmaking. In his account, democratic input into the judicial arena exists. It is fostered through the activity of interest groups as amicus curiae (Latin for “friends of the court”). In Friends of the Supreme Court: Interest Groups and Judicial Decision Making, Collins demonstrates how popular interests are brought to bear on decisionmaking in the highest court of the land.

However, before delving into an examination of the various ways in which amici influence decisionmaking, Collins evaluates a critical issue for the democratic question. What if groups filing amicus briefs are predominantly of one ideological persuasion or if, as is the case in the other branches of government, they speak chiefly for the “haves” rather than the “have-nots”? In Chapter 3, he tests the pluralist and elitist perspectives to show that in the last six decades conservative and liberal causes have been equally represented in briefs filed with the Court. Furthermore, the types of amici run the gamut from government to unions and even individuals.

The informational value of the briefs is the centerpiece of the theoretical framework developed. In analyzing their content, the author concludes that briefs provide information pertaining to legal authorities, policy questions, and constitutional issues otherwise unavailable to justices. Rather than public opinion or the preferences of the other branches channeled via the briefs, it is this novel information that accounts for the effects amici have on the Court. But in what ways does the information contained in briefs influence the choices justices make?

To answer this question, Collins integrates theories from a wide range of disciplines and employs state-of-the-art research methods. In Chapter 4, the attitudinal and the legal models of judicial decisionmaking are juxtaposed with mutually exclusive predictions derived from each. To determine which of the two prevails, a key test is developed: How do justices respond to briefs endorsing an ideological position incongruent with their own? The empirical results unambiguously support the prediction of the Legal Persuasion Model—ideological proclivity aside, justices are influenced by the content of the brief. In other words, notwithstanding the justice's ideology, he or she will be more likely to cast a conservative (liberal) vote the greater the number of conservative (liberal) briefs are filed. Typical to other parts of the book as well, Collins interprets the findings of a rather complicated statistical concept (here, an interaction term in a probit model) in a compelling and intuitive way, using plots and tables.

Apart from being exemplary in its adherence to the highest standards of the social scientific method (e.g., systematically testing refutable and mutually exclusive hypotheses), the research presented in this chapter has important theoretical implications. It sheds new light on our understanding of the role of law in Supreme Court decisionmaking. In addition, it clarifies the constraints on justices' ability to engage in motivated reasoning, key to the attitudinal model. But the effect on votes on the merits is only the first of three examined in the book.

Drawing on studies in psychology, economics, and anthropology, in Chapter 5 Collins examines the effect of amicus briefs on yet another aspect of judicial decisionmaking: its consistency. In a nutshell, briefs increase the number of possible options available to justices in their rulings. Due to cognitive overload, this would lead to increased inconsistency, with its normative and empirical implications. Inconsistency is modeled as the variance in the votes justices cast. The findings indicate that the novel information in the briefs renders justices more likely to rethink their preconceptions. Consequently, variability increases. Chapter 6 brings the discussion of the democratic question full circle when it analyzes the effect of amicus briefs this time on the Court's democratic output—separate opinions registered by individual justices. Since they raise novel issues and reduce the cost of writing separately, amicus briefs increase the likelihood that a justice would write or join a dissenting, special concurring, or regular concurring opinion.

The informational value of the briefs is clear from the analyses presented. Yet particularly in the theory in Chapters 5 and 6, the main function of the information is to obfuscate and overload justices' cognitive processes, which results in inconsistency and more separate opinions. However, the confusing effect of briefs may be overstressed. In fact the function of briefs may be to eschew obfuscation and clarify what used to be convoluted issues for the justices. Briefs may serve to elucidate legal questions, illuminate policy implications, and explain vague issues. By reading such briefs, justices would be able to think more (rather than less) clearly about the questions presented. That said, the final behavioral effect might be similar—thinking more clearly about a case, justices might realize, for example, that the questions it presents involve four rather than just two policy dimensions. This may result in a greater number of separate opinions or more variance in decisionmaking. But the indistinguishable behavioral upshot is a result of cognitive clarity rather than cognitive overload.

Friends of the Supreme Court is an exceptional work of scholarship. Social scientists from several disciplines as well as legal researchers will appreciate the theoretical depth and interdisciplinary approach. The book has obvious appeal for courses in judicial politics and public law. What makes this volume particularly appealing for students is the way the author elegantly interweaves cutting-edge methods of inference with examples from actual cases argued before the Supreme Court. This book is bound to become an authoritative source for scholars of judicial behavior and interest groups and for students at the graduate and undergraduate levels.