Measuring the Importance of Supreme Court Opinions

The following is by Professor David Stras of the University of Minnesota Law School. Professor Stras will occasionally provide commentary on the Court’s business and alert readers to significant academic developments regarding the Supreme Court.

A group of political scientists (James Fowler, Timothy Johnson, James Spriggs, Sangick Jeon, and Paul Wahlbeck) have posted a new article on SSRN entitled “Network Analysis and the Law: Measuring the Legal Importance of Supreme Court Precedents,” which is available here. Using network analysis, which is a methodology commonly used to map and analyze computer networks (like the World Wide Web), the authors treat the cases of the Supreme Court of the United States as nodes in a network, connected by citations or links to one another. The methodology, as applied to the Supreme Court, measures two characteristics for each node: first, all precedents cited by a case (also called outward citations), and second, all subsequent citations to that case (also called inward citations). Outward citations demonstrate whether a particular case is well-founded in the law, and inward citations show whether a case is influential. Together, these two characteristics appear to be the best measure of case importance to date.

Notably, the model is predictive of whether the Supreme Court will cite a particular precedent in any given year. For instance, a one standard deviation increase in the value of the inward importance of a case increases the probability of a case being cited in any given year by 73.8%. By contrast, other measures of case importance, such as whether a case appears in the New York Times, perform much more poorly in their predictive ability. The inward and outward importance scores for a particular case are similarly predictive of whether a lower court will cite that precedent in any given year.

Of particular value to Supreme Court practitioners and Court watchers, the authors include a table (Table 2 on page 34) that lists separately the 20 most outwardly and inwardly important cases as of 2005. The five most inwardly important cases of 2005 are Cantwell v. Connecticut, Schneider v. State, New York Times v. Sullivan, Thornhill v. Alabama, and NAACP v. Button. The five most outwardly important cases of 2005 are First National Bank v. Belotti, Griswold v. Connecticut, Buckley v. Valeo, Dennis v. United States, and Young v. American Mini Theaters Inc. The list of cases in both categories provides an excellent reading list for Supreme Court practitioners, and indeed, those are the cases that are most likely to be found in a Supreme Court opinion for 2005 (and likely 2006 and 2007 as well). One interesting, unanswered question from their research is whether citation and discussion of inwardly or outwardly important cases in a brief makes the argument more persuasive to the Court, as together the Justices determine a case’s importance in the citation network.