“What is Judicial Ideology, and How Should We Measure it?”

That was the title of an excellent symposium piece by Josh Fischman and David Law last year that highlighted the limited scholarly work that has been done to effectively define and measure judicial ideology, particularly for judges not serving on the Supreme Court. Academics who are not engaged in empirical work relevant to the courts are often to surprised to find out just how crudely ideology is measured by law scholars and political scientists. There really are only two existing measures of the judges serving on the federal courts other than the Supreme Court: political party of the appointing President and Judicial Common Space Score. Every major study in empirical legal studies for decades examing members of the judiciary has relied upon one of those two metrics to determine the ideologies of federal judges (with most studies using the party of the appointing President).

Using the President’s party reduces ideology to a simple binary score – either a judge is “liberal” or “conservative.” Notably, using the President’s party, recent and current Justices Clarence Thomas, John Paul Stevens, Sandra Day O’Connor, Antonin Scalia, Samuel Alito, Harry Blackmun, and David Souter are ideological equals. In a nomination battles, the measure is essentially useless since whoever the President nominates is given the exact same score.

Judicial Common Space Scores (developed and maintained by Lee Epstein, Andew MartinJeffrey Segal, and Chad Westerland) have been praised as a needed improvement upon using the President’s party. Those scores rely upon the norm of senatorial courtesy by integrating the voting records, based upon NOMINATE scores (developed and maintained by Royce Carroll, Jeff Lewis, James Lo, Nolan McCarty, Keith Poole, and Howard Rosenthal), of the home state Senators of the judge nominated. While, the Common Space Scores move beyond a binary construction, it is unclear whether they represent a true improvement over the President’s party. Fischman & Law’s study examined 9th Circuit asylum cases and found that the Common Space Scores were only marginally better at forecasting the results in such cases.

Common Space Scores still use the President’s party to determine the direction of the ideology (liberal or conservative) meaning that all of the Justices listed above are still considered conservative by using the measure. Justice Sonia Sotomayor presents an interesting case of how these scores work in practice. She was first appointed by President George H.W. Bush to the district court. She was then elevated to the appellate court by President Clinton. And President Obama completed her judicial journey by nominating her to the Supreme Court. Before Clinton acted, both of the leading measures would have classified her as conservative. If she had never been elevated further, she would have forever been considered conservative in academic study. However, with Clinton and Obama’s actions, she instantly became liberal. This was not because of any decisions she issued while on the district court. It was simply due to the politics of the President. Both of the leading measures are forever frozen in time at the time of nomination and do not account for situations where: 1) a judge drifts in ideology over time (Justice Blackmun); 2) a President was mistaken or did not care about a judge’s ideology (Justice Souter); 3) a President focuses on a limited number of issues in nominating a judge without considering the overall ideology of the judge; or 4) a President appoints a judge of the opposite party for political reasons. It is also unclear whether Senatorial courtesy really is strong enough norm to substantiate increased validity of the Common Space Scores.

Given these known limitations, outsiders often wonder why these measures are used. In my next post, I will talk about the differing techniques that have been or could be used to measure judicial ideology. Given the difficulties with each of those approaches, it should be a bit clearer why the Common Space Scores and appointing President’s party measure dominate empirical research.

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5 Responses

  1. A.J. Sutter says:

    What about other forms of ideology, such as a judge who uses law & economics-based reasoning? There are both liberal and conservative judges who fall into that pot.

  2. Corey Yung says:

    Hi A.J.,

    I will talk about the unidimensionality in a future post as it is an important point. Certain methods lend themselves to multidimensional measurements better than others. One difficulty, though, is while most people have a pretty good idea of what “liberal” and “conservative” mean, other dimensions are more difficult to nail down. A unidimensional spectrum also can capture the other dimensions to the degree that they intersect conservative and liberal thought. For example, in my measure, Judge Easterbrook shows up as very conservative. In contrast, Judge Posner shows up as a moderate leaning toward slightly liberal. On a unidimensional spectrum, that probably makes sense. Judge Easterbrook’s law and economics approach will tend to lead him to agree with conservatives more. In contrast, Judge Posner’s pragmatism would tend to make him a moderate as it might point in either direction in a particular case. Nuance is lost with unidimensionality, but the results still allow for more sophisticated interpretation. It also should be noted that at least for the United States Supreme Court, prior research has shown that the unidimensional political spectrum covers a large majority of the ideology of the Justices. That shouldn’t be terribly surprising as judges are nominated by a President from one of two parties and confirmed by a Senate that is essentially composed of two parties. And judges are drawn from a society that largely structures itself around two parties. That most ideologies of judges can be mapped on a unidimensional spectrum would be the expected result.


  3. Bryan Gividen says:


    I am assuming your working paper covers the same issues you will bring up in your next post. After reading through it, I was still skeptical of using the district judge’s political disposition as a measuring stick for going in or outside of party lines, primarily in unanimous cases. Those situations seem to be a clear legal question as opposed to an ideology question. (Using the baseball analogy, a down the middle strike would be a 9-0 opinion while a 5-4 split would be an inside corner near the knees – more about the individual umpire and less about “rules.”) Would you be able to cover that in a response or in one of your subsequent posts?

  4. A.J. Sutter says:

    Thanks for your reply. I’d meant to use scare quotes, à la “liberal” and “conservative”, to reflect the purely conventional nature of those labels. Even the identification of those labels with the political parties is shaky, because of the same unidimensionality you mention.

  5. Corey Yung says:

    Hi Bryan,

    I will be covering the issue you raise in a future post. It is definitely a tricky issue. However, given that 98.4% of the cases in my dataset are unanimous opinions, I think it is a stretch to say that all or even a substantial majority of those are “easy” cases. The high rate of agreement might be largely due to panel effects, strategic incentives, or norms of consensus. My measure attempts to properly weight the various instances of disagreement among panelists and with the district judges so that the 3-0 affirmances do not have the same significance as 2-1 reversals (particularly in criminal cases with a deferentail standard of review).