by Paul M. Collins Jr. New York: Oxford University Press. 2008. 248pp. Cloth $60.00/£41.00. ISBN: 9780195372144.

Reviewed by Paul Chen, Department of Political Science, Western Washington University. Email: paul.chen [at]


In FRIENDS OF THE SUPREME COURT, Paul Collins makes an outstanding contribution to the literature on interest group litigation by expanding our empirical and theoretical knowledge of the influence of amicus briefs on the voting behavior of Supreme Court justices. Specifically, on whether law has any influence on judges’ decisions or whether judges are basically politicians in robes whose decisions reflect their policy preferences, Collins finds the results of his research “overwhelmingly supportive of the legal persuasion model” (p.110).

Early in his book, Collins notes that the scholarly consensus – that “amicus briefs, with the exception of those briefs filed by the Solicitor General, have little measurable influence on the justices’ decision making on the merits” (p.5) – flies in the face of statements to the contrary made by the justices themselves, and also contradicts the behavior of interest groups, who file amicus briefs in nearly every case reviewed by the Supreme Court, ostensibly to influence the Court’s decision. He also notes that previous studies lacked generalizability, suffered from selection bias, were time-bound, or used “imprecise or incomplete measures” (pp.6-7). The most serious weakness of these studies was failing to provide an adequate theory explaining why amicus briefs should influence the Court (p.9). Collins fills this theoretical gap by incorporating the concept of information overload into his analysis to help “explain how political actors with ideological goals respond to persuasive communication that sometimes supports and sometimes is contrary to these goals” (p.12).

The book addresses three main questions: (1) whether amicus briefs influence the ideological direction of justices’ votes; (2) whether amicus briefs influence the consistency of justices’ votes (i.e. do the briefs make a justice’s voting more consistent or less consistent across cases); and (3) whether amicus briefs influence justices’ decisions to write or join separate opinions (pp.10-11). Each of these questions is addressed, respectively, in Chapters 4, 5, and 6.

The “central controversy” tackled by scholars of the Court concerns the extent to which judicial behavior is influenced by legal as opposed to ideological factors (p.80). Stated more bluntly, is it law or politics, the legal model or the attitudinal model? In Chapter 4, Collins integrates his research into this central question by formulating two competing hypotheses that predict “how amicus briefs are expected to influence the individual justices’ decision making consistent with these two divergent approaches to judicial choice” (p.82). [*105]

Behavioral studies have traditionally defined the legal model as entailing three key tenets: the plain meaning approach to legal interpretation, the framers’ (or legislators’) intent, and precedent. In contrast, Collins tests a “legal persuasion” aspect which differs from these tenets which seem to imply that “justices engage in mechanical jurisprudence” or “robotically apply precedent and other legal rules to any given case to reach an objectively correct decision” (p.83). The hypothesis for his legal persuasion model, which presumes that the influence of amicus briefs on the justices’ decision making is not mediated by their ideologies, predicts that “[a]s the number of liberal [or conservative] amicus curiae briefs increases, so too will the likelihood of observing a liberal [or conservative] vote,” regardless of the justices’ ideology (p.92). The rationale is that judges, “consistent with their legal training and as unbiased decision makers” (p.84), “explore alternative legal perspectives . . . [t]o reach what they believe to be the correct decision” (p.89). Amicus briefs, which “present alternative or reframed legal arguments” are meant to persuade the justices of the legal correctness of the amici’s position (p.90).

Whereas the legal persuasion model views all justices as unbiased seekers of the correct legal decision, the attitudinal model views justices as influenced by amicus briefs depending on whether the information in the briefs reinforces or undermines the pursuit of their policy preferences. This view is supported by research in social psychology showing that we tend to discount or ignore information that contradicts our predetermined attitudes, while we view as being more persuasive information that reinforces our attitudes (pp.92-93). Collins’ attitudinal congruence hypothesis predicts that “[a]s the number of liberal [or conservative] amicus curiae briefs increases, so too will the likelihood of observing a liberal [or conservative] justice cast a liberal [or conservative] vote” (p.94).

Note that “the predictions are identical, although the theoretical reasons for them are not.” The legal persuasion congruence model views justices, regardless of their ideology, as seeking information to apply the law to a case correctly, but the attitudinal congruence model views justices as seeking information, based on their ideology, to maximize their policy preferences. The way to determine “which theory best explains the justices’ behavior comes from an examination of how a liberal ([or] conservative) justice responds to an increasing number of conservative ([or] liberal) briefs.” The attitudinal model hypothesizes that no correlation exists between an increasing number of liberal (or conservative) briefs and the likelihood that justices will vote in the direction of those briefs (because the justices would ignore the briefs and simply vote their policy preferences). The legal persuasion model, however, hypothesizes a positive correlation between the two: as the number of liberal (or conservative) briefs increases, so too the likelihood of justices voting in the direction of those briefs, regardless of their ideology (pp.97-98).

The legal persuasion model predicts 66% of the votes (p.106). In cases involving asymmetric amicus participation – i.e. where the number of amicus briefs supporting one party [*106] outnumber those supporting the other party – Collins finds the influence of amicus briefs “rather dramatic”:

With regard to conservative briefs, the results indicate that compared with a case in which a single conservative brief is filed (and a single liberal brief), when 10 conservative briefs are filed (and one liberal brief), the most liberal justice in the data . . . is 6% more likely to vote conservatively. This increases to 14% for the vast majority of the Court . . . and is slightly attenuated for the most conservative justices in the sample, who are 12% more likely to vote conservatively in this situation. The results are virtually identical for liberal amicus briefs: the most liberal justice in the data is 6% more likely to cast a liberal vote as the number of liberal briefs moves from 1 to 10, while the majority of the Court is about 14% more likely to cast a liberal vote (pp.109-110).

“[W]ith the exception of three extremely conservative justices for short periods of their careers,” Collins finds that the justices’ ideology does not mediate their reception of the information in the amicus briefs, and concludes that “the legal persuasion model best explains the influence of amicus briefs in the Court.” This shows that “judicial decision making on the Court is more than a function of the justices’ ideological preferences.” Collins highlights the point that “by persuading the justices to adopt positions consistent with the legal argumentation in the briefs, amicus briefs provide us with insight into one way in which the law matters to Supreme Court decision making” (p.114, emphasis in original).

In Chapter 5, Collins tests the hypothesis that increasing the number of amicus briefs filed in a case will decrease the consistency of justices’ voting across cases. The concept of information overload, taken from other disciplines that study decision making, states that an inverse relationship exists between the complexity of a decision and the likelihood of reaching a correct decision. Therefore, as the amount of information that a decision maker must consider increases – i.e. as the decision’s complexity increases – the certainty of his or her reaching a correct decision based on the available information decreases. Collins’ model predicts 66.6% of cases (p.127), confirming his hypothesis that an increase in the number of amicus briefs in a case decreases the consistency of justices’ voting across cases. “By bringing new issues to the justices’ attention, the amici make it difficult for the justices to determine what the correct application of the law is in any given case” (p.120). (In Chapter 3, based on an analysis of fifty-two amicus briefs filed in twelve cases containing a total of 121 arguments, Collins found that over 70% of the amicus briefs provided information not contained in the parties’ briefs, and that every amicus brief provided additional legal authorities not cited in the parties’ briefs [p.66]).

In Chapter 6, Collins tests the hypothesis that increasing the number of amicus briefs in a case will increase the likelihood of a justice writing or joining a separate opinion (p.154). By providing, in the form of additional information and arguments, a “substantial basis from which a justice can cultivate a separate opinion,” amicus briefs reduce the resource costs of writing concurring or dissenting opinions, thus making it more likely that justices will do so (p.151). “[E]ven after [*107] controlling for more conventional influences” – e.g. justices’ ideological proximity to the majority opinion writer, justices’ institutional role on the Court, a case’s legal complexity and its political salience (pp.155-159) – Collins finds strong support for his hypothesis, noting that the effect “is especially enhanced in cases attracting a large number of briefs” (p.161).

The significance of this finding is that the inclusion of additional legal arguments via the submission of amicus briefs decreases the consistency or stability of justices’ voting across cases, whereas voting consistency is enhanced when judges decide cases based on extreme ideological biases. This “conundrum” presents for Collins “a most unsettling tradeoff”: “If we value [legal] consistency, this can be achieved through the appointment of ideologically extreme judges who will regularly vote to etch their preferences into law and seldom deviate from this behavior. If we value reasoned and neutral deliberation, provided by legalist judges, we must recognize that their behavior will be marked by instability due to the inherent indeterminacy of the law” (p.177).

Chapter 2 mainly provides background information on interest group litigation, and surveys the research on amicus activity by organized groups. In Chapter 3, Collins discusses, more specifically, amicus participation in Supreme Court cases, and mentions several noteworthy empirical findings, of which I will mention two. One concerns the ideological bias of the interests participating in Supreme Court litigation: contrary to the perception that during certain decades Supreme Court litigation has been dominated by liberal and progressive interests, throughout all four Court eras under analysis (1946-2001) “the overall correlation between the average number of liberal and conservative briefs [submitted per case per term] is an astonishing .97” (p.55). The fact that the number of conservative (or liberal) amicus briefs does not increase during conservative (or liberal) Court eras “provides compelling evidence that amici file briefs in cases that genuinely touch on their interests, rather than ‘cherry pick’ cases for the purposes of appearing efficacious” (p.56).

The other finding concerns the range of organized interests represented in amicus briefs. Collins finds that the range of organized groups participating in Supreme Court litigation “reflects a much more diverse set of interests” than lobbying in other branches, suggesting that the justices receive a broader range of views via the submission of amicus briefs. This pluralism holds true not only for the positions advocated by amici (i.e. liberal and conservative) but also for the types of organizations represented (e.g. corporate interests, minority interests, even ad hoc organizations of individuals) (p.63). When reviewing criticisms of legal instrumentalism in Chapter 7, Collins suggests that the plurality of views aired before the Court should give us some comfort, because it serves to “overcom[e] this troubling perspective of interest group instrumentalism [by] enabl[ing] judges to hear from a diverse spectrum of organizations who present conflicting views of the public interest” (p.170).

In summarizing his theoretical and empirical findings in Chapter 7, Collins [*108] affirms that “attitudes are likely the primary influence on judicial decision making.” But he notes that his research provides strong evidence of a “bottom-up approach” in which “justices carefully review all of the available evidence and argumentation for the purpose of reaching a sound legal decision.” This is also supported by research from management science and social psychology showing that “individuals who are required to justify their decisions . . . are especially likely to be motivated by accuracy goals.” “[T]he bottom-up approach to judicial decision suggests that opinions might well reveal factors that motivate judicial choice” (pp.176). Collins then considers competing theories that posit the influence of public opinion on, or separation of powers considerations by, the Supreme Court as providing adequate explanations for his findings, and ultimately rejects them (pp.177-182).

Collins tackles the central question in the field of public law using a research design that tests theoretically-grounded hypotheses based on the stated normative goals of justices. By measuring the influence of amicus briefs on individual justices’ votes rather than on case outcomes, he is able to test whether the justices’ ideologies mediate their reception of information from amicus briefs. He carefully circumscribes his findings, noting key issues not addressed in his research, including whether certain types of arguments, certain types of amici, or certain types of organized interests are more influential than others (pp.183-184). Most importantly, he disclaims any attempt to explain how or why law and legal arguments matter – that is, what is the “exact mechanism under which amicus briefs influence the justices’ decision making” (p.177).

While Collins’ regression models have shown that amicus briefs do influence justices’ votes, it remains the work of qualitative studies to show how and why this is so. Nevertheless, Collins’ research has taken a big step in the right direction: first, by showing systematically and empirically that legal arguments do influence justices’ voting behavior; and second, by testing a “legal persuasion” model that differs from the traditional legal model posited by attitudinalists who fail to understand that the indeterminacy of law does not necessarily make the purported influence of law either delusional or a sham. Collins’ hypotheses are based on the stated normative goal of justices to make decisions that most closely align with their views of the correct application of law. Although justices may disagree whether certain precedents require a particular outcome in a case, the subjectivity of their judgment does not necessarily make their decisions unprincipled or arbitrary.

The findings of Collins’ research also carry normative significance for the rule of law by showing that the law matters to justices when they decide cases. Not only has he provided a rigorous and theoretically-informed methodology to test the influence of amicus briefs on the justices’ decision making, but his findings provide empirical support for the assumption underlying most qualitative analyses of the Court – namely, that law matters. Collins, in closing, enthusiastically encourages methodological pluralism, recognizing that, because “the study of the law is [*109] inherently interdisciplinary, . . . we must be attentive to the fact that no single discipline” – or methodology – “has a monopoly on legal decision making” (p.185).

© Copyright 2009 by the author, Paul Chen.