Pamela C. Corley1 Amy Steigerwalt2 Artemus Ward3
1Southern
Methodist University
2Georgia State University
3Northern Illinois University



Media accounts routinely paint a
portrait of a deeply ideologically
divided Court:
“An ideologically divided Supreme
Court wrestled Wednesday” with
an Establishment Clause case
(Biskupic 2010).
“The Supreme Court yesterday
split along a familiar ideological
battle line in its consideration of
the Voting Rights Act” (Barnes
2009).



Pritchett was the first political scientist to use
quantitative methods to study judicial behavior.
He argued that unanimity results when “the facts and
the law are so clear that no opportunity is allowed for
the autobiographies of the justices to lead them to
opposing conclusions” (1941, 890).
He then proceeded to ignore unanimous decisions in
his analysis of judicial behavior since he simply
assumed that legal factors sufficiently explained
unanimity.

Segal and Spaeth (1993, 2002) do not provide
an analysis of—nor an explanation for—
unanimous cases. According to one scholar,
“If we exclude a large proportion of cases
from our analysis, claiming that we cannot
predict or explain them because of their
unanimity, we are certainly missing a large
part of the behavior of the Supreme Court.
We are then left guessing what happened in
those cases” (Benesh 2003, 124).

Consensus results from clarity and certainty in applying
the law
◦ One answer is legally stronger than any other.

If the law is clear, justices’ ability to vote their attitudes is
constrained.
◦ Law and attitudes simultaneously operate in every case, and the
degree of influence each exerts exists along a continuum.

If the level of legal certainty is low, the constraining force
of law is minimal or even absent.
◦ Justices’ personal policy preferences determine the outcome of
the case and the chance of unanimity is low.

If level of legal certainty is high, law acts to constrain
justices’ ability to vote their preferences.
◦ Law predominates and the chance of unanimity is high.

Thus, the level of legal certainty either constrains or
enables the operation of attitudes.
◦ Barak (2005): “Judicial discretion…[reflects] uncertainty in law.”





According to Baum: “The easy case gives precedence to
legal considerations, because judges are directed to the
result that has greater legal support….[J]udges are unlikely
to reach a decision consistent with their policy preferences
when they would have great difficulty justifying it in legal
terms.”
Recognize that all cases decided by Supreme Court are
“difficult.”
“Even in hard cases, there is usually one side that emerges
as slightly stronger than the other” (Kerr 2009).
When a case contains “appreciable legal ambiguity,”
judicial discretion is unfettered and justices can freely rely
on their attitudes (Kerr 2009)
“The region of legal uncertainty is where judges render
decisions with the least legal guidance, and where judges’
particular mix of legal and social views has the most
leeway and impact” (Tamanaha 2010, 190).
Legal
Considerations
Attitudes
Decision
Legal
Considerations

Richards and Kritzer (2002)
◦ Justices, using their attitudes, create jurisprudential
regimes which then guide future behavior.

Bailey and Maltzman (2008)

Bartels (2009)
◦ Isolate the influence of non-policy factors on
decision-making, showing justices are constrained
by stare decisis, judicial restraint, and strict
interpretations of First Amendment
◦ Examines how some legal rules act to constrain
justices while others grant justices a significant
amount of discretion




Focused primarily on question of whether
unanimous decisions increase legitimacy of
Court.
Numerous studies have analyzed breakdown in
“norm of consensus.”
Grossman (1967) argued that attitudinal factors
influenced even unanimous votes while Goldman
(1969) argued that “objective” case situations
offer little room for attitudes to influence
justices’ voting in unanimous cases.
Brenner and Arrington (1987) found that liberal
outcomes dominated unanimously decided cases.

Hensley and Johnson (1998) examined 1986-1990 terms,
finding that unanimous cases more likely:
◦
◦
◦
◦
◦

routine cases
liberal cases
non-civil liberties and rights cases
cases involving federal action
cases where less time is spent between oral argument and decision
date.
Edelman, Klein, and Lindquist (2008) and Roy and Songer
(2011) focus on whether the attitudinal model explains
unanimous decisions of the Supreme Court. Both studies
conclude that the justices’ attitudes do not adequately
explain how the justices reach consensus, and
subsequently conclude that legal or jurisprudential
concerns must therefore drive these Supreme Court
decisions. They do not, however, provide direct support for
the influence of legal factors.



Given all of the information presented to the justices,
how certain or uncertain is the legal answer to the
question presented in a particular case?
We use five discrete variables, each coded
dichotomously, to capture the various facets of each
case which might suggest a higher or lower level of
legal certainty
Each variable is coded such that a 1 signals a factor
indicating higher legal certainty. We then combine
these five variables to create an index, scaled 0 to 5,
with 0 reflecting the lowest possible level of legal
certainty and 5 representing the highest possible
level of legal certainty.
1.
Legally Noncomplex – Non-complex cases without
multiple legal questions or issues in dispute lead to
more certainty and less ambiguity for the justices.
◦ We counted the total number of legal issues and laws each
case addressed. We then coded all cases addressing two or
less legal issues and laws as 1 and all cases addressing more
than two legal issues and laws as 0.
2.
Lack of Amicus Participation
◦ Presence of amicus briefs expands the scope of conflict.
“[A]mici make it difficult for the Justices to determine the
correct application of the law in each case” (Collins
2008: 152).
◦ We coded this variable 1 if one or no amicus briefs were filed
in the case and 0 if more than one amicus brief was filed.
3.
Lack of Legal Dissensus Among Lower Court Judges
 Read each lower court opinion and coded whether opinion was
unanimous or contained a dissent, a concurrence, or both.
 Determined which judges heard the case and whether each judge voted
with majority in all respects, concurred or dissented.
 Determined party of appointing president for federal court judges and
party of judge or appointing governor for state court judges (proxy for
judicial ideology)
 For federal 3-judge panels, if dissenting judge was of opposite party as
the two judges in majority coalition, variable coded 0. If dissenting
judge was of the same party as one of the judges in the majority
coalition, variable coded 1.
 For state high courts, and en banc circuit court panels, if majority
coalition was composed of members of one party, and all dissenters
were members of opposite party, variable coded 0. If either majority
coalition or dissenting coalition was ideologically incongruent, variable
coded 1.
 If panel itself was ideologically congruent, and there was a dissent,
variable coded 1.
 If case contained a concurrence, variable coded 1.
 No dissent or concurrence, variable coded 0.
4.
Statutory Interpretation. Statutes are generally more
detailed and less ambiguous than constitutional
provisions.
◦ Coded 1 if the case decided a statutory issue, 0 otherwise.
5.
Lack of Legal Conflict. The existence of a conflict
between lower courts suggests there are at least two
different viewpoints about which answer is the
strongest.
◦ To distinguish conflict cases that are more likely to arise from a
legal versus an ideological dispute, we focus on whether they
involve an important or significant question. If the issue is an
important one, it is more likely that the lower court judges are
deciding based on ideology rather than law. We therefore
hypothesize that when a case lacks a conflict altogether, or involves
a conflict over an important issue, the level of certainty should be
higher and consensus easier to achieve.
◦ Accordingly, we code all cases that lack a conflict or involve an
important conflict as 1; all those that involve a conflict in the lower
courts over a relatively “unimportant” question we code as 0.



All cases appealed from a lower federal court
which were granted certiorari, orally argued,
and decided by the Supreme Court during the
1953-2004 terms.
Unit of analysis is the individual case.
Dependent Variables
◦ Whether vote in each case was unanimous
 40% unanimous
◦ Whether vote in each case was unanimous or highly
consensual
 51% decided with one dissent or complete unanimity
55%
8%
45%
15%
11%
% of Decided Cases
35%
One Dissenting Vote
Unanimous
25%
44%
37%
38%
Warren
Burger
15%
5%
-5%
Court
Rehnquist

Attitudinal influences
◦ Degree of ideological dispersion
 Absolute value of the difference between median justice’s
Martin-Quinn score and most ideologically distant
justice’s Martin-Quinn score
◦ Reversal and Extreme Lower Court Decisions
 Supreme Court is more likely to reach a unanimous or
highly consensual decision when the Court is reversing,
when there is an ideologically extreme lower court
decision, and when both factors are present.
 Compared ideology of lower court panel with ideology of
Supreme Court, identified ideologically extreme judges and
justices, and coded case as “extreme” if any member of lower
court panel was more extreme than most ideologically
extreme Supreme Court justice

Strategic influences
◦ Chief Justice Writes the Majority Opinion
 Chief may work harder to command a unanimous Court.
◦ Median Justice Writes the Majority Opinion
◦ Median justice may be more likely to compromise,
accommodate, and otherwise find common ground.
◦ Altered Precedent/Declared Statute Unconstitutional
 Because the literature is mixed on whether the justices are likely
to be more consensual or ideological when altering precedent or
striking down laws, we do not make a prediction as to the
direction of the effect such an action may have on the justices’
ability to reach consensus.
◦ Solicitor General is a Party to the Case
 Previous research shows that the SG wins the vast majority of its
cases. We hypothesize that the SG will not only win but win big
in terms of unanimity.

Institutional Context
◦ Chief Justice (Burger Court, Rehnquist Court) – Chiefs can exhibit both task
and social leadership in creating a harmonious Court. We created dummy
variables for each chief justice and we use Chief Justice Warren as the
baseline for comparison.
◦ Addition of Syllabus – The Burger Court marked the end of the institutional
norms of acquiescence and notation. We suggest that it was the Court’s
decision in 1971 to include a syllabus at the start of every opinion
specifying each justice’s vote. Decisions during or after 1971 are coded 1;
those prior to 1971 are coded 0.
◦ Formalization of Dissent Assignment – Following Justice Douglas’ departure
in 1975, Justice Brennan began the practice of the senior justice in the
dissent coalition formally assigning the dissent. We suggest that this
practice provides incentives for justices to dissent and for dissenting
opinions to be issued. We code decisions handed down during or after 1975
as 1 and those before 1975 as 0.
◦ Docket Size – The number of cases granted by the Court was cut in half
during Rehnquist’s tenure. We posit that the shrinking docket allows for
greater resources to be devoted to cultivating individual expression, thereby
undermining consensus.
◦ Number of Law Clerks – Research suggests that law clerks influence the
justices’ decisions to issue separate opinions. The number of clerks per
associate justice was doubled from one to two in 1947, went to three in
1970, and four in 1974. The Chief can have one more clerk than the
associates and retired justices also get a clerk. We include a variable for the
total number of law clerks each term and hypothesize that their increasing
number and responsibilities further dissensus.

Case Factors
◦ Issue Area – Ideological preferences in civil liberties cases
may be more defined and deeply held than in cases
involving government powers or economic activity issues.
◦ Political Salience – Salient cases are more likely to be
decided ideologically. Salient cases are those that appeared
on the front page of the New York Times that day after the
decision.
◦ Liberal Decision – Previous research shows that liberal
decisions dominate unanimously decided cases – even
during conservative courts.
◦ Time to End of Term – Prior research shows that time
pressures appear to effect opinion consensus (less time =
less likely to write concurrences). We expect to see more
opinion consensus when time is short. We count the
number of days between the date of oral argument for each
case and the end of the Court’s term (generally July 1).
Variable
Model 1:
Unanimous
Decisions
Model 2:
Unanimous or
Highly Consensual
Decisions
Coefficient (R.S.E)
Coefficient (R.S.E)
.122 (.038)***
.128 (.038)***
Legal Influences
Level of Legal Certainty
Attitudinal Influences
Ideological Polarization
Extreme Lower Court Decision
-.097 (.051)*
-.005 (.197)
Reversed Lower Court Decision
.110 (.079)
Extreme Lower Court Decision
X Reversed
-.162 (.248)
Note: * p < .05, ** p <.01, ***p < .001
-.053 (.050)
.003 (.192)
.180 (.078)*
-.044 (.242)
Variable
Model 1:
Unanimous
Decisions
Model 2:
Unanimous or
Highly Consensual
Decisions
Coefficient (R.S.E)
Coefficient (R.S.E)
.275 (.118)**
.294 (.117)**
Strategic Influences
Chief Justice Writes Maj. Opinion
Median Justice Writes Maj. Opinion -.165 (.144)
-.316 (.138)**
Altered Precedent
-.130 (.270)
-.237 (.258)
Declared Statute Unconstitutional
-.246 (.260)
-.246 (.246)
.067 (.074)
.069 (.073)
.003 (.211)
-.071 (.206)
-.095 (.170)
-.177 (.166)
Docket Size
.000 (.002)
-.002 (.002)
Number of Law Clerks
.010 (.025)
.037 (.025)
Rehnquist Court
.393 (.425)
-.230 (.416)
Burger Court
.131 (.341)
-.209 (.332)
SG Party
Institutional Context
Addition of Syllabus
Formalizing Dissent Assignment
Model 1:
Unanimous
Decisions
Model 2:
Unanimous or Highly
Consensual Decisions
Coefficient (R.S.E)
Coefficient (R.S.E)
Government Powers Issue
.596 (.094)***
.680 (.093)***
Economic Issue
.492 (.086)***
.508 (.085)***
Political Salience
-.615 (.120)***
-.589 (.110)***
Liberal Decision
.555 (.074)***
.468 (.073)***
-1.423 (.609)**
-1.253 (.591)**
Variable
Case Factors
Constant
N
3,245
Note: * p < .05, ** p <.01, ***p < .001
p-values reflect one-tailed tests if directionally hypothesized.
R.S.E. = robust standard error clustered on case citation.
3,245
Change in Variable Value
Predicted
Probability of a
Predicted
Unanimous or
Probability of Highly
a Unanimous Consensual
Decision
Decision
Legal Certainty (min → max)
+57%
+50%
Ideological Dispersion (min → max)
-37%
n.s.
Associate Justice Writes → Chief Justice
Writes
+21%
+19%
n.s.
-19%
Civil Liberties Issue → Government
Powers Issue
+49%
+44%
Civil Liberties Issue → Economic Issue
+39%
+32%
Non-salient Case → Salient Case
-38%
-33%
Conservative decision → Liberal
decision
+45%
+30%
Non-Median Justice Writes → Median
Justice Writes
Change in Variable Value
Predicted
Probability of a
Predicted
Unanimous or
Probability of Highly
a Unanimous Consensual
Decision
Decision
Legal Certainty (min → max)
.201→.316
.290→.436
Ideological Dispersion (min → max)
.346→.218
n.s.
Associate Justice Writes → Chief Justice
Writes
.272→.330
.383→.454
n.s.
.383→.311
Civil Liberties Issue → Government
Powers Issue
.272→.404
.383→.550
Civil Liberties Issue → Economic Issue
.272→.379
.383→.507
Non-salient Case → Salient Case
.272→.168
.383→.256
Conservative decision → Liberal
decision
.272→.394
.383→.497
Non-Median Justice Writes → Median
Justice Writes
Variable
Low Level of Legal
Certainty
High Level of Legal
Certainty
Ideological Dispersion
-.186 (.071)**
-.015 (.072)
Variable
Low Level of Legal
Certainty
High Level of
Legal Certainty
Ideological Dispersion
-.137 (.069)*
-.021 (.072)
Variable
Model 1
Model 2
Model 3
Coefficient (R.S.E)
Coefficient (R.S.E)
Coefficient (R.S.E)
Legal Influences
Level of Legal Certainty
.206 (.044)***
.176 (.040)***
.166 (.039)***
Attitudinal Influences
Ideological Polarization
Extreme Lower Court
Decision
Reversed Lower Court
Decision
Extreme Lower Court
Decision X Reversed
-.107 (.057)*
.080 (.216)
-.085 (.053)
-.082 (.051)
-.093 (.205)
.002 (.199)
-.016 (.089)
.045 (.081)
.066 (.080)
.065 (.273)
-.016 (.258)
-.064 (.250)
Model 1: Fully Unanimous Opinion (no separate opinions).
Model 2: Fully Unanimous or Highly Consensual Opinion (one concurrence)
Model 3: Fully Unanimous or Highly Consensual Opinion (one concurrence or one
dissent with one justice dissenting)
Note: * p < .05, ** p <.01, ***p < .001
Model 1
Model 2
Model 3
Coefficient (R.S.E)
Coefficient (R.S.E)
Coefficient (R.S.E)
.101 (.137)
.147 (.123)
.118 (.119)
Median Justice Writes
Maj. Opinion
-.303 (.171)
-.245 (.149)
-.335 (.146)*
Altered Precedent
-.159 (.333)
-.247 (.292)
-.427 (.284)
-1.599 (.528)**
-.662 (.300)*
-.441 (.276)
-.065 (.085)
.001 (.077)
-.030 (.075)
Addition of Syllabus
.036 (.244)
.128 (.221)
-.012 (.215)
Formalizing Dissent
Assignment
-.087 (.193)
-.138 (.176)
-.217 (.171)
Docket Size
-.001 (.002)
.002 (.002)
.002 (.002)
Number of Law Clerks
-.025 (.028)
.007 (.026)
.023 (.025)
Rehnquist Court
.676 (.463)
.248 (.428)
-.043 (.418)
Burger Court
.337 (.364)
-.111 (.340)
-.225 (.332)
Variable
Strategic Influences
Chief Justice Writes
Maj. Opinion
Declared Statute
Unconstitutional
SG Party
Institutional Context
Variable
Model 1
Model 2
Model 3
Coefficient (R.S.E)
Coefficient (R.S.E)
Coefficient (R.S.E)
Case Factors
Government
Powers Issue
.720 (.105)***
.648 (.096)***
.764 (.094)***
.714 (.099)***
.596 (.089)***
.656 (.087)***
Political Salience
-.761 (.158)***
-.781 (.132)***
-.875 (.126)***
Liberal Decision
.376 (.084)***
.517 (.077)***
.407 (.075)***
Economic Issue
Time Left until
End of Term
-.001 (.001)*
-.001 (.001)
-.001 (.001)
Constant
-1.051 (.681)
-1.686 (.634)**
-1.492 (.615)**
N
3,391
3,391
Note: * p < .05, ** p <.01, ***p < .001
p-values reflect one-tailed tests if directionally hypothesized.
R.S.E. = robust standard error clustered on case citation.
3,391
Change in Variable Value
Model 1
Model 2
Model 3
+143%
+102%
+85%
-46%
n.s.
n.s.
Non-Median Justice Writes → Median
Justice Writes
n.s.
n.s.
-22%
No Declaration of Unconstitutionality
→ Declaration of Unconstitutionality
-77%
-42%
n.s.
End of Term Close → End of Term Far
Away
-12%
n.s.
n.s.
Civil Liberties Issue → Government
Powers Issue
+76%
+59%
+63%
Civil Liberties Issue → Economic Issue
+76%
+53%
+53%
Non-salient Case → Salient Case
-49%
-48%
-50%
Conservative decision → Liberal
decision
+36%
+45%
+32%
Legal Certainty (min → max)
Ideological Dispersion (min → max)
Change in Variable Value
Model 1
Model 2
Model 3
Legal Certainty (min → max)
.087→.211
.140→.283
.185→.342
Ideological Dispersion (min → max)
.219→.119
n.s.
n.s.
Non-Median Justice Writes → Median
Justice Writes
n.s.
n.s.
.280→.218
No Declaration of Unconstitutionality
→ Declaration of Unconstitutionality
.157→.036
.225→.130
n.s.
End of Term Close → End of Term Far
Away
.228→.200
n.s.
n.s.
Civil Liberties Issue → Government
Powers Issue
.157→.277
.225→.357
.280→.455
Civil Liberties Issue → Economic Issue
.157→.276
.225→.345
.280→.429
Non-salient Case → Salient Case
.157→.080
.225→.117
.280→.140
Conservative decision → Liberal
decision
.157→.214
.225→.327
.280→.369
Variable
Low Level of Legal
Certainty
High Level of Legal
Certainty
Ideological Dispersion
-.131 (.084)
-.112 (.079)
Note: * p < .05, ** p <.01, ***p < .001
p-values reflect one-tailed tests if directionally hypothesized.
R.S.E. = robust standard error clustered on case citation.
Variable
Low Level of Legal
Certainty
High Level of Legal
Certainty
Ideological Dispersion
-.136 (.075)
-.068 (.074)
Note: * p < .05, ** p <.01, ***p < .001
p-values reflect one-tailed tests if directionally hypothesized.
R.S.E. = robust standard error clustered on case citation.
Variable
Low Level of Legal
Certainty
High Level of Legal
Certainty
Ideological Dispersion
-.117 (.072)*
-.082 (.074)
Note: * p < .05, ** p <.01, ***p < .001
p-values reflect one-tailed tests if directionally hypothesized.
R.S.E. = robust standard error clustered on case citation.
Level of legal certainty constrains and enables the ability of
justices to vote according to personal policy preferences.
High level of legal certainty, Court more likely to achieve a
unanimous or highly consensual decision.
Low level of legal certainty, Court less likely to achieve a
unanimous or highly consensual decision.
Court is a political institution and a legal institution.
Variable
Unanimous
Unanimous or Highly
Consensual
Legally Noncomplex
.250 (.091)**
.180 (.087)*
Lack of Amicus Participation
.001 (.083)
.053 (.082)
Lack of Legal Dissensus
Among Lower Court Judges
.220 (.080)**
.237 (.077)***
Statutory Issue
.102 (.078)
.164 (.076)**
Lack of Legal Conflict in
Lower Courts
.014 (.085)
-.082 (.084)
Variable
Model 1
Model 2
Model 3
Legally Noncomplex
.510 (.113)***
.389 (.096)***
.279 (.093)**
Lack of Amicus
Participation
.174 (.096)*
.073 (.086)
.111 (.084)
Lack of Legal Dissensus
Among Lower Court
Judges
.103 (.092)
.179 (.083)**
.196 (.081)**
Statutory Issue
.229 (.090)**
.234 (.081)**
.280 (.079)***
Lack of Legal Conflict in
Lower Courts
.059 (.095)
-.018 (.087)
Model 1: Fully Unanimous Opinion (no separate opinions).
Model 2: Fully Unanimous or Highly Consensual Opinion (one
concurrence)
Model 3: Fully Unanimous or Highly Consensual Opinion (one
concurrence or one dissent with one justice dissenting)
Note: * p < .05, ** p <.01, ***p < .001
-.135 (.086)