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Lee Epstein
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Lee Epsteing Ethan A.H. Shepley Distinguished University Professor
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IDEOLOGICAL DRIFT AMONG SUPREME COURT JUSTICES: WHO, WHEN, AND HOW IMPORTANT?

Published in 2007. Northwestern University Law Review 101 (Fall): 1483-1542.

Lee Epstein
Andrew D. Martin
Kevin M. Quinn
Jeffrey A. Segal

When President George W. Bush declared that his Supreme Court nominee, Harriet E. Miers, was ``not going to change, that 20 years from now she'll be the same person with the same philosophy that she is today," no one should have been shocked. To the contrary: The President was merely reiterating a claim dominant in public and scholarly discourse over the Supreme Court---that justices come to the Court with robust ideological outlooks and do not veer from them over the course of their tenure. Nonetheless, and despite the commonplace nature of the claim, it is not without its share of skeptics; indeed, some commentators now contend that ideological drift among Supreme Court justices is not just possible but likely.

Using systematically developed data and sophisticated statistical tools, we address the question of whether justices remain committed to a particular doctrinal course over time. The results, as it turns out, could not be clearer: Contrary to the received wisdom, virtually all justices serving since 1937 grew more liberal or conservative during their tenure on the Court.

Finding that change is the rule, not the exception, we develop the implications of our findings for the justices' appointment to the Court and the doctrine they develop once confirmed. We show, for example, that Presidents hoping to create a lasting legacy in the form of justices who share their ideology can be reasonably certain that their appointees will behave in line with contemporaneous expectations—at least during the justice's first term in office. But because most justices fluctuate soon thereafter, Presidents emphasize ideology to the neglect of other considerations—such as the advancement of their political party's electoral ambitions—at their own peril.

We conclude with a discussion of the prospects for legal change among the justices of the Roberts Court. Here we consider two plausible scenarios, one in which the justices remain relatively true to their current doctrinal inclinations and another in which members drift. Either way, we find that legal change may be possible—a finding that defies contemporary expectations about the inertia of justices and, by implication, the Court in the absence of membership turnover.

Click here for the article.
Click here for the data (Stata .dta file) (posted on 3.8.07) (data also available on Andrew D. Martin's website). Note: Martin and Quinn recommend using the posterior mean (post_mn) as the estimate the ideal point of each justice in each term.