Political Analysis Advance Access originally published online on May 22, 2007
Political Analysis 2007 15(3):324-346; doi:10.1093/pan/mpm011
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Network Analysis and the Law: Measuring the Legal Importance of Precedents at the U.S. Supreme Court
Department of Political Science, University of California, San Diego, Social Sciences Building 383, 9500 Gilman Drive #0521, La Jolla, CA 92093-0521
Department of Political Science, University of Minnesota, Twin Cities, 1414 Social Sciences Building, 267 19th Ave. South, Minneapolis, MN 55455
e-mail: trj{at}umn.edu
Department of Political Science, Washington University in St. Louis, Campus Box 1063, One Brookings Drive, St Louis, MO 63130
e-mail: jspriggs{at}artsci.wustl.edu
Department of Political Science, Stanford University, 616 Serra Street, Encina Hall West, Room 100, Stanford, CA 94305-6044
e-mail: sjeon{at}stanford.edu
Department of Political Science, George Washington University, 1922 F Street, N.W. Suite 401, Washington, DC 20052
e-mail: wahlbeck{at}gwu.edu
e-mail: jhfowler{at}ucsd.edu (corresponding author)
We construct the complete network of 26,681 majority opinions written by the U.S. Supreme Court and the cases that cite them from 1791 to 2005. We describe a method for using the patterns in citations within and across cases to create importance scores that identify the most legally relevant precedents in the network of Supreme Court law at any given point in time. Our measures are superior to existing network-based alternatives and, for example, offer information regarding case importance not evident in simple citation counts. We also demonstrate the validity of our measures by showing that they are strongly correlated with the future citation behavior of state courts, the U.S. Courts of Appeals, and the U.S. Supreme Court. In so doing, we show that network analysis is a viable way of measuring how central a case is to law at the Court and suggest that it can be used to measure other legal concepts.
Authors' note: We appreciate the suggestions of Randy Calvert, Frank Cross, Pauline Kim, Andrew Martin, Richard Pacelle, Jim Rogers, Margo Schlanger, Amy Steigerwalt, and participants in the Workshop on Empirical Research in the Law at Washington University in St Louis School of Law. We presented former versions of this article at the 2006 meeting of the Midwest Political Science Association, Chicago, April 20–23; the 2006 meeting of the Southern Political Science Association, Atlanta, GA, January 5–7; and the 2006 Empirical Legal Studies Conference, Austin, TX, October 27–28.