Peremptory Challenges and Jury Selection

I examine how peremptory challenges, which are vetoes that attorneys may use to reject prospective jurors, affect jury composition. The purpose of peremptory challenges is to eliminate biased jurors; however, I show that under the two most common rules used in the United States, peremptory challenges actually increase the probability of juries composed entirely of members on one extreme or another of some ideological spectrum. I then show that it is not possible to design a peremptory-challenge procedure that unambiguously makes such juries less likely. I show that if unanimity is required for conviction, the distribution of juror types is symmetric about some mean type, and each attorney has the same number of challenges, then challenges benefit the prosecution.