Scholar’s highlight: The ideology of Supreme Court opinions and citations

Political scientists have studied the Supreme Court and found that many Justices appear highly ideological in their decisions.  Some Justices vote consistently in a conservative direction, while others are consistently liberal.  This may be no great surprise to Court watchers, but lawyers often fail to come to grips with the Court as an ideological institution, not just a legal one. However, the political science studies on voting are typically quite facile, examining only the outcome of the case and categorizing it as “liberal” or “conservative.”

The outcome of a case before the Supreme Court doesn’t mean very much, deciding only the dispute between the parties.  The key to a Supreme Court decision lies in the nature of the opinion.  It is the opinion that sets the law, and a liberal result may be accompanied by a more or less liberal justification.  Yet it is the nature of that justification that is crucial to the law.  Because lower courts carefully adhere to Supreme Court precedent, it is the opinions that need study, as individual outcomes may be misleading.  For example, in Roth v. United States, the Court reached a conservative result, but it did so with an opinion that empowered many future liberal decisions.

In my article, The Ideology of Supreme Court Opinions and Citations, I set out to measure the ideology of opinions based upon the nature of their citations in subsequent opinions.  Citations are where opinion influence might be expected to show up in the law.  My database began shortly after World War II, and I limited the analysis to important cases, reported on the first page of the New York Times.  My theory was that the most liberal opinion would tend to be cited more as support of future liberal opinions and have relatively few citations in future conservative opinions.  By my theory, a more liberal opinion would have fewer qualifications that enabled it to be manipulated in pursuit of the opposite ideology.  Of course, many factors – not least changes in the Court’s agenda – influence the number of future citations, although not necessarily their ideological valence.

Because I am writing on unfurrowed ground, I considered a number of different measures. These included the nature of the citation (followed, explained, etc.) and whether the citation was in a majority opinion or a dissent.  Then I compiled the citations to the opinions on different scales.  First, I looked at simple citations.  The conservative case with the most conservative citations was Gregg v. Georgia, while the liberal case with the most liberal citations was Miranda v. Arizona.  But this is merely the absolute number of ideological citations, and Miranda was commonly cited in support of conservative outcomes.  An alternative scale might be the ratio of liberal to conservative opinions, but this was not very helpful, dominated by decisions with few citations (and zero or one of the opposite ideology).

I developed a concededly arbitrary influence score giving greater weight to stronger treatments (followed) and reducing points when a case was used either by the opposite ideology or by the same ideology in dissent, indicating the opinion was relevant but could not control the subsequent outcome.  By this measure, the most powerful liberal opinion was NAACP v. Button, and the most powerful conservative opinion Harris v. McRae.  Liberal opinions were significantly more powerful than conservative ones in this particular database, but this was probably an artifact of then-progressive opinions on civil rights and free speech that are now widely accepted.

The key question is “why are some opinions more powerful and influential?”  I looked at the identity of the authoring justice.  The opinions of Justices Black, Douglas, and Warren were by far the most liberal, but opinions of Justice Brennan were much more moderately so, perhaps evidencing he was more of a compromiser and not so liberal as often suggested.  The author of the most conservative opinions was Justice Powell, notably more so than Justices such as Rehnquist and Scalia.

These findings, though intriguing, are but preliminary.  I’m employing a commonly used word analysis program for opinions to see if language choices matter.  It wasn’t designed for the law, but legal dictionaries could be created.  Perhaps more (or fewer) citations affect an opinion’s power.  The surface is only being scratched here, and I’m quite open to any ideas from the readership.

Frank Cross is Professor of Law at the University of Texas.