The Median Justice on the U.S. Supreme Court
Published in 2005. North Carolina Law Review 83 (5): 1275-1322.
Andrew D. Martin
Kevin Quinn
Lee Epstein
Abstract
Black's "Median Voter Theorem" now figures prominently and crucially in a wide array of research on the United States Supreme Court, from studies on the nomination and confirmation of Justices, to investigations into the Court's resolution of disputes, to analyses of its impact on the hierarchy of justice. Nonetheless, and regardless of the substantive focus of the investigation, the question of how to locate the median Justice looms large. Because all extant answers have their share of problems, we set out to develop a more compelling approach-one that relies on methods developed by Martin and Quinn. Via this approach we derive a systematic accounting of the Justice with the highest (posterior) probability of having served as the median for each Term since 1937. In what follows, we (1) introduce the Martin-Quinn method, (2) explain why it represents an improvement over previous efforts, and (3) offer two contemporary applications-both of which assess emerging pieces of wisdom about the Court: that (a) the median Justice (Sandra Day O'Connor) has moved to the "left" or, at least, has grown more moderate in recent Terms, and (b) President George W. Bush will be able to "remake" the Court.
Click here for the article (in .pdf).
The Martin-Quinn Ideal Point estimates are available in an Appendix to the article. Here are other data necessary to replicate our analyses (also available at the Ideal Points for the U.S. Supreme Court web site, maintained by Andrew Martin and Kevin Quinn).
Justice dataset: contains the ideal point estimates and other quantities of interest for each justice in each term (.txt version, Stata version, Excel version, SPSS version)
Court dataset: contains court-specific quantities, including the estimated location of the median justice (.txt version, Stata version, Excel version, SPSS version)
If you use these data, please cite: Andrew D. Martin and Kevin M. Quinn. 2002. "Dynamic Ideal Point Estimation via Markov Chain Monte Carlo for the U.S. Supreme Court, 1953-1999." Political Analysis. 10: 134-153.