North Carolina Law Review

University of North Carolina School of Law

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Examining the Evolution of Legal Precedent Through Citation Network Analysis

96 N.C. L. Rev. 227 (2017) 

 

Precedent----the rule that judges rely on past decisions in adjudicating the disputes in front of them----is a fundamental part of the American legal system. Precedent plays a role in understanding how the law evolves, determining how the courts behave, and helping legal search engines recommend relevant cases. Studying the network of citations between judicial opinions can provide an empirical perspective on precedent. This Comment examines the Supreme Court citation network and the Federal Appellate citation network. Building upon previous empirical legal work, this Comment uses network analysis to provide insights into the role of precedent in the courts and to identify important cases in various contexts. Vertex centrality metrics, which measure how important a vertex is in a network in different ways, provide a way of quantifying the notion of importance of a case in a citation network. There are many kinds of vertex centrality metrics. This Comment further develops a methodology to evaluate vertex centrality metrics in an evolving network based on how predictive a metric is of future citations. This methodology is able to identify several possibly surprising results regarding court behavior and behavior of the metrics themselves. In particular, it unexpectedly shows that the number of cases cited in an opinion is a stronger predictor of whether that opinion will be cited in the future than the number of times that opinion has already been cited by other opinions. 

 

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