Academic journal article Northwestern University Law Review

THE USE AND LIMITS OF MARTIN-QUINN SCORES TO ASSESS SUPREME COURT JUSTICES, WITH SPECIAL ATTENTION TO THE PROBLEM OF IDEOLOGICAL DRIFT[dagger]

Academic journal article Northwestern University Law Review

THE USE AND LIMITS OF MARTIN-QUINN SCORES TO ASSESS SUPREME COURT JUSTICES, WITH SPECIAL ATTENTION TO THE PROBLEM OF IDEOLOGICAL DRIFT[dagger]

Article excerpt

In their new article, Lee Epstein, Jeffrey Segal, Andrew Martin, and Kevin Quinn investigate changes in behavior by Supreme Court Justices.1 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 authors 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' behavior are more common than has been generally supposed; and that the authors' 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 Justices demonstrated their views before joining the Court.

I.

The authors claim to show that the policy preferences of most Supreme Court Justices change while they are on the Court. The force and importance of this result depend, of course, on the strength of the method used to produce it. Their article relies on what they call "Martin-Quinn" scores for the Justices, but where those scores come from and just what they mean are not explained; the reader is referred to other articles for discussion of those issues.4 Referring the reader elsewhere is perfectly all right in principle, of course, but in this case the explanations in those other articles turn out to be hard to follow-or at least hard for me to follow. The fault no doubt is mine, as I am all thumbs with mathematics; then again, that fault is widely shared among the apparent audience for the authors' new article: lawyers and others arguing about who ought to be put onto the Supreme Court. For them, a clearer account in words of how the authors reached their conclusions is much needed. Otherwise there is a risk that readers will ignore the authors' findings because they don't understand them, or accept the authors' conclusions on faith because the findings have emerged from a black box that is mysterious but looks impressive. I mean no disrespect to the authors or to their ability to explain themselves. I just view it as a case where they speak a slightly different language than some members of their audience.

In hopes of making the operation of the authors' methods more transparent to the non-mathematician, then, I read the prior work of Professors Martin and Quinn in which they present their methods; more importantly, they were then so kind, patient, and collegial as to let me to ask them many questions, for which I hereby record my thanks. I will now explain my understanding of their method as plainly as I can. I apologize in advance to anyone who finds that I am belaboring the obvious, and to Martin and Quinn for any inaccuracies I commit in the course of simplifying and explaining their approach.

The Martin-Quinn method keeps track of only one thing: whether a Justice voted to affirm or reverse in a case.5 The method does not pay attention to what the case was about; the method itself has nothing to do with politics or ideology (or, for that matter, law). All it knows are things like this: in the first case decided last year, Justices A, B, C, and D voted to affirm and Justices E, F, G, H, and I voted to reverse. …

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