I develop a new measure of interpersonal influence on the U.S. Supreme Court. Following Altfeld and Spaeth, I define influence as “the act of producing an effect on the behavior of another without the use of coercion, authority, or political control.” I propose a measure of influence based on the number of times a justice cites her colleagues’ concurring and dissenting opinions. My analysis proceeds in two stages. First, I verify that this citation-based measure is a valid method of gauging influence. From there, I use this measure to help explain justice behavior in two pivotal stages of the Supreme Court’s decision-making process: oral arguments and opinion assignments. The results demonstrate that a citation-based measure of influence can help explain and predict behavior on the Supreme Court.

Is the decision-making of Supreme Court justices influenced by extraneous factors beyond law and policy? We explore this question by examining attorney-induced laughter during oral arguments in cases heard by the Court. Drawing on theories of political psychology and social cognition, we posit that laughter serves as a positive affective cue that might favorably dispose justices (albeit subconsciously) to the side causing the laughter. Analyzing oral argument transcripts during the 1986-93 terms, we find that the side causing more instances of laughter is more likely to win the votes of individual justices, even while controlling for other legally and politically relevant factors. We further find that the effect of laughter is conditional-it exerts a heightened persuasive power on ideologically congruent justices, in noncomplex cases, and when the legal argumentation is of higher quality. Our research thus contributes to the growing literature on personal and emotional aspects of judicial decision-making and, specifically, the emerging scholarly interest in the role of humor during Supreme Court oral arguments.