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I'm a law professor at the University of Iowa. My research focuses on:
Evidence Law
Antitrust Law
Law and Economics

Photo of Sean P. Sullivan

My research merges traditional legal analysis with economics and statistics. I am particularly interested in the use of game theory, probability theory, and experimental economics as tools of doctrinal analysis. I write on topics in Evidence Law, Antitrust Law, and Law and Economics.

Evidence Law

The thesis of my recent work in Evidence Law is that probability theory can be used to clarify the fact-finding process and the rules of evidence. In one of my papers, Probative Inference from Phenomenal Coincidence, I use simple numerical models to illustrate errors and imprecision in common articulations of the lack-of-accident theory in Rule 404(b)(2) of the Federal Rules of Evidence, and equivalent state codes. Another of my papers, A Likelihood Story, tackles the century-old puzzle of deciding how to conceptualize the fact-finding process. The paper shows frustration with decades of efforts to describe fact-finding in terms of probabilities can be avoided by instead modeling fact-finding in terms of the different but related idea of likelihoods. This revised understanding clarifies the common structure of the different burdens of persuasion and offers normative suggestions for improving fact-finding by drawing attention away from the subjective beliefs of the fact-finder.

Antitrust Law

My work in Antitrust Law seeks to improve the fit between legal analysis and economic theory. For example, in What Structural Presumption? I show how a seemingly innocuous bit of legal formalism has subtly displaced economic analysis in an important aspect of merger analysis. In a similar vein, one of my recent working papers, The Logic of Market Definition, seeks to clarify how market definition should be conducted in antitrust cases. By clarifying the economic content of the market concept, this paper is able to identify several common fallacies in market definition. These include the tendency to view markets as natural or corporeal entities; the tendency to think of markets as concepts independent of a theory of anticompetitive injury; and the tendency not to miss how relevant markets may differ for different theories of harm, even within a common case or controversy.

Law and Economics

Another arm of my research involves the use of game theory as a tool of legal analysis across a variety of subject areas. An illustration is Powers, But How Much Power?, a paper in which I use principal-agent models and other concepts in game theory to propose a novel interpretation of the constitutional nondelegation principle. Another example is a current working paper, Insincere Evidence, in which I and a coauthor use simple economic modeling to illustrate underappreciated relationships between substantive rules and burdens of persuasion as well as ways in which burdens of persuasion modulate incentives to comply with legal standards. Another example is my larger interest in the use of experimental economics as a tool of legal analysis. I apply experimental methods to understanding settlement delay in Why Wait to Settle? and survey broader uses of experimental economics in law as coauthor of the experimental economics chapter of the Oxford Handbook of Law and Economics.