Ideal Justice: Mathematicians judge the Supreme Court
Erica Klarreich
The U.S. Supreme Court?already in the news this week for its decisions on
affirmative action?is highlighted in a scientific journal. The court is driven
by politics far less than Congress is, a new analysis suggests.
Lawrence Sirovich, a mathematician at Mount Sinai School of Medicine in New
York City, calculated that the current Supreme Court of nine judges behaves as
if it were made up of about 4.68 "ideal" judges?adjudicators who make their
decisions completely independently of each other. To put that figure in
perspective, Sirovich says, a court with a strict liberal-conservative divide
would behave as if it had only one judge because all decisions would be
determined purely by which faction made up the majority.
"The analysis shows that there is a great deal of independence among the
justices," he says. Sirovich reports his findings in the June 24 Proceedings
of the National Academy of Sciences.
In contrast, earlier studies of the U.S. Congress by political scientists
Keith Poole of the University of Houston and Howard Rosenthal of Princeton
University confirmed the conventional wisdom that members of Congress usually
vote along fairly strict party lines.
Sirovich's approach strips the legal content from the decisions, whereas
previous studies of the Supreme Court have often been driven by preconceptions,
says law professor Yochai Benkler of New York University. "This is a novel mode
of analysis that is innocent of hypotheses and simply looks at what is," he
says.
To assess judicial independence, Sirovich examined the Supreme Court's
rulings over the past 8 years in light of a measure of information content
developed in the 1940s by mathematician Claude Shannon. Roughly, the more
independent the judges, the less predictable their rulings, so the greater the
information contained in each ruling.
Coalitions drive down the number of ideal judges. "Suppose we have two judges
who always vote the same way," Sirovich says. "Then, from the point of view of
information, we have eight justices, not nine."
During the past 8 years, Justices Antonin Scalia and Clarence Thomas voted
the same way more than 93 percent of the time, and Justices Ruth Bader Ginsburg
and David Souter voted the same way more than 90 percent of the time. The fact
that the number of ideal judges is as high as 4.68 is encouraging, Sirovich
says.
Sirovich's work is an interesting analysis, Poole says. However, he cautions,
many other studies suggest that the justices are heavily swayed by political
viewpoints. "Only about 9 percent of their choices aren't explained by a simple
liberal-to-conservative ordering," he says. "The court is very ideological."
Benkler says that, from Sirovich's analysis, it's clear that "judges do a
whole lot more than follow the party line. But particular judges with particular
worldviews do align."
In the new work, Sirovich applied the pattern-analysis techniques that he had
used previously to study turbulent fluid flow, face recognition, and the
structure of the brain.
"That's what tickled me most about this paper," says mathematician Steven
Strogatz of Cornell University. "The beauty of mathematics is in realizing that
some things are the same problem, even though they don't appear to be."
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References:
Sirovich, L. 2003. A pattern analysis of the second Rehnquist
U.S. Supreme Court. Proceedings of the National Academy of Sciences
100(June 24):7432-7437. Abstract available at http://www.pnas.org/cgi/content/abstract/100/13/7432.
Further Readings:
Ellenberg, J. 2001. Growing apart. Slate (Dec. 26).
Available at http://slate.msn.com/id/2060047/.
Poole, K.T., and H. Rosenthal. 2001. D-NOMINATE after 10
years: A comparative update to Congress: A Political-Economic History of Roll
Call Voting. Legislative Studies Quarterly 26(February):5-29.
Available at http://voteview.uh.edu/prapsd99.pdf.
______. 1997. Congress: A Political-Economic History of
Roll Call Voting. New York: Oxford University Press. See http://www.oup-usa.org/docs/0195055772.html.
Sources:
Yochai Benkler
Vanderbilt Hall
40 Washington Square
South
New York, NY 10012-1066
Keith T. Poole
Department of Political
Science
University of Houston
Houston, TX 77204-3011
Lawrence Sirovich
Laboratory of Applied
Mathematics
Department of Biomathematical Sciences
Mount Sinai School of
Medicine
One Gustave Levy Place
New York, NY 10029
Steven H. Strogatz
Department of Theoretical and Applied
Mathematics
Cornell University
Ithaca, NY 14853-1503
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