Friends You Can Trust: A Signaling Theory of Interest Group Litigation Before the U.S. Supreme Court

Date01 September 2017
Published date01 September 2017
Friends You Can Trust: A Signaling Theory of
Interest Group Litigation Before the U.S. Supreme
Lucia Manzi Matthew E.K. Hall
How do interest groups influence U.S. Supreme Court justices to vote in favor
of their preferred outcomes? Following prior research on the influence of the
Solicitor General, we develop and expand on the signaling theory of interest
group influence via amicus curie briefs. We argue that an interest group’s
ideological reputation and the nature of the ideological signal it sends in its
brief both function as powerful heuristics that convey information to the justi-
ces depending on the justices’ own ideological preferences. When an organi-
zation files an amicus brief advocating for an outcome seemingly contrary to
its traditional preferences (i.e., an unexpected signal), this signal should be
more noticeable and credible than a signal in accordance with a group’s con-
ventional views (i.e., an expected signal). However, unexpected signals should
have greater influence on justices who share the brief filer’s preferences. We
test our signaling theory on the terms from 1991 through 2002. We find that
unexpected signals (but not expected signals) are associated with Supreme
Court voting, and the influence of unexpected signals appears to be particu-
larly strong among justices who share the ideological preferences of the brief
The rising number of amicus curiae briefs filed in the U.S.
Supreme Court has attracted increased scholarly attention to the
effect of interest group advocacy on the Court. The substantial
and growing participation by amici suggests that interest groups
believe these activities are influential, and empirical evidence sug-
gests they might be right. Earlier research shows that Supreme
Court justices rely so heavily on information in amicus briefs,
that they often signal their need for these documents to interest
groups (Hansford and Johnson 2014). Moreover, previous works
have found that amicus briefs do not just influence the justices’
final decisions on the merits of a case (Box-Steffensmeier et al.
The authors presented an earlier version of this article at the 2014 Midwest Political
Science Association Annual Meeting. The authors wish to thank Ben Denison, Paul J. Hig-
son, Ana Petrova, Nate Sumaktoyo, and Dwight B. King for their help and support. The
authors would also like to thank the four anonymous reviewers for their helpful
Please direct all correspondence to Lucia Manzi, Department of Political Science, Uni-
versity of Notre Dame, Notre Dame, IN 46556; email:
Law & Society Review, Volume 51, Number 3 (2017)
C2017 Law and Society Association. All rights reserved.
2013; Collins et al. 2013, 2015), they also affect the justices’ deci-
sion to hear a case in the first place, namely to “grant certiorari”
to a legal case coming from a lower court
(Caldeira and Wright
1988; Owens and Black 2011). In addition, other studies suggest
that amicus briefs may have a significant effect on the likelihood
of dissenting opinions (Collins 2008a). Finally, the influence of
amicus briefs appears to extend to all justices across the ideologi-
cal spectrum (Collins 2008b). Nevertheless, the nature of their
influence remains the topic of much disagreement among schol-
ars. Why are amicus curiae briefs so influential? Do all interest
groups stand the same chance of influencing all of the justices, or
are some groups better positioned to influence certain justices in
certain ways?
We address these questions by extending Baily, Kamoie, and
Maltzman’s (2005) signaling theory beyond the Solicitor General
to all interest groups filing amicus curie briefs in the U.S.
Supreme Court. Specifically, we argue that amicus participation
functions as a heuristic signal: Every amici sends a signal to mem-
bers of the court, which includes heuristics, or “mental shortcuts,”
based on the filer’s ideological preferences in relation to the justi-
ce’s preferences and the brief ’s ideological position on the case.
These heuristic signals help the justices deal with the high num-
ber of amicus briefs by allowing them to quickly and easily iden-
tify credible information.
Consequently, an interest group’s ability to influence a justice
depends on the group’s ideology, the justice’s ideology, and the
nature of the ideological signal sent by the group. Justices are
particularly inclined to trust interest groups that share their ideo-
logical preferences and interest groups advocating outcomes con-
trary to their traditional ideological preferences. Amicus briefs
should be especially likely to influence justices when both condi-
tions are present; i.e., a justice and brief filer share ideological
preferences and the brief filer sends an unexpected ideological
signal. As a result, influential legal advocacy only partially
depends on an interest group’s inherent features (i.e., its ideol-
ogy); amicus influence also depends on a specific litigation strat-
egy (sending unexpected signals) and the nature of the signal
receivers (the justice’s ideology).
The U.S. Supreme Court offers an ideal venue to test our sig-
naling theory of interest group influence for several reasons.
First, the highly formalized and routinized process of amicus fil-
ing renders lobbying activities easy to observe and measure.
The U.S. Supreme Court chooses the cases it wants to hear. In order for a case to be
accepted for review by the Supreme Court, a majority of justices has to vote in favor of
accepting the case, or to “grant certiorari,” in the legal jargon of the Supreme Court.
Manzi & Hall 705

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