Everything you always wanted to know about the Martin-Quinn Scores, but were afraid to ask

On the SCOTUS Blog, David Stras posts an “ask the author” set of questions for Washington University’s Andrew Martin on, of course, the Martin-Quinn scores for Supreme Court Justices. The introduction and first two questions/answers are below the fold.

This edition of “Ask the Author” features a discussion with Andrew Martin, who is a professor of law and chair of the political science department at Washington University in St. Louis. Andrew has done some very influential work on the Supreme Court, including co-authoring a paper on ideological drift of Supreme Court Justices, see here, that will appear in issue four of the Northwestern University Law Review. Andrew is also well-known in political science and empirical circles for his influential Martin-Quinn scores, a technique for measuring the ideology of Supreme Court Justices that he co-developed with Kevin Quinn of Harvard University. For more information on Andrew, please see his personal webpage.

1. What are Martin-Quinn scores? How are they different from other measures of judicial ideology, such as merely looking at the characterization of a Justice’s ideology in prominent newspapers such as the New York Times?

Martin-Quinn scores (http://mqscores.wustl.edu) are measures that place justices on a common ideological continuum. They do so for each justice in each term since 1937, and are estimated using merits votes derived from the Supreme Court Judicial Database. The scores we produce differ from those derived from newspaper coverage at the time of a justice’s nomination/confirmation in a couple of keys respects. First, the measures are based on actual judicial behavior. Second, the scores are dynamic, allowing the position of each justice to evolve over time. The method employed allows us to make over-time comparisons. Third, the Martin-Quinn scores have been shown to classify votes well across all legal issues, while other measures are typically limited to civil rights and civil liberties cases.

2. How are these scores useful for the non-academic? What do they tell us about the Court?

The scores are useful to anyone who is interested in the politics or decision making patterns of the high court. The scores can be used to understand the politics of the Supreme Court at any point of time, in essence, providing political context to any decision of interest. The scores can also be used to isolate the pivotal (or median) justice in any given term. Many surmise that Justice Kennedy is the pivotal member of the current court; the Martin-Quinn scores provide a scientific basis for that conclusion.

For the rest of the questions and answers, you’ll have to check out the post on SCOTUS Blog.