101 Nw. U. L. Rev. 1891 (2007)
The Use and Limits of Martin-Quinn Scores to Assess Supreme Court Justices, with Special Attention to the Problem of Ideological Drift

handle is hein.journals/illlr101 and id is 1899 raw text is: Copyright 2007 by Northwestern University School of Law            Printed in U.S.A.
Northwestern  University Law  Review                                Vol. 101, No. 4
THE USE AND LIMITS OF MARTIN-QUINN SCORES
TO ASSESS SUPREME COURT JUSTICES, WITH
SPECIAL ATTENTION TO THE PROBLEM OF
IDEOLOGICAL DRIFT'
Ward Farnsworth*
In their new article, Lee Epstein, Jeffrey Segal, Andrew Martin, and
Kevin Quinn investigate changes in behavior by Supreme Court Justices.'
They conclude that the policy preferences of most Justices change during
their careers, and suggest that this should cause Presidents to reconsider the
use of nominations to try to change the direction of the Court.2 I find the
authors' evidence and analysis interesting, but am not yet convinced that
any rethinking is in order by the people who pick Justices or care about
their selection. I will begin with a general discussion of the model-the
Martin-Quinn scores-that the authors use to generate their findings. It is
an ingenious method that is attracting some wider interest,3 but its basis and
workings have not yet been presented in a non-technical fashion that is
likely to be understood well by a legal audience. One goal of this Essay is
to explain it in lay terms. Then I will consider the particular claims the au-
thors make and, finally, their more general thesis about the predictability of
behavior by Supreme Court Justices. My two conclusions, in short, are that
the authors have not proven that consequential surprises in the Justices' be-
havior are more common than has been generally supposed; and that the au-
thors' advice to Presidents (and others interested in the selection of Justices)
is premature: the behavior of some Justices is more predictable than that of
others, and this itself can often be predicted by asking how firmly the Jus-
tices demonstrated their views before joining the Court.
t This Essay was previously published in the Northwestern University Law Review Colloquy on
April 2, 2007, as Ward Farnsworth, The Use and Limits of Martin-Quinn Scores to Assess Supreme
Court Justices, with Special Attention to the Problem of Ideological Drift, 101 Nw. U. L. REV.
COLLOQUY 143 (2007), http://www.law.northwestem.edu/lawreview/colloquy/2007/11/.
. Professor and Nancy Barton Scholar, Boston University School of Law. Many thanks to Andrew
Martin and Kevin Quinn for discussing their work with me at some length, and to Quinn for comments
on an earlier version of this Essay; thanks as well to Andrew Kull for comments and discussion.
I Lee Epstein et al., Ideological Drift Among Supreme Court Justices: Who, When, and How Im-
portant?, 101 Nw. U. L. REV. 1483 (2007).
2 Id. at 1526-28.
3 Id. at 1503 n.87.

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