Jury Deliberation and the Hung Jury Paradox

In Williams v. Florida 399 U.S. 78 (1970), the U.S. Supreme Court decided a case concerning the minimum number of jurors required at trial under the Sixth and Fourteenth Amendments. The Court ruled that the a jury comprised of fewer than twelve jurors was constitutionally acceptable. In an effort to speed deliberation and reduce the rate of mistrials, eleven states have subsequently adopted juries of fewer-than-twelve in felony trials, and forty states have diminished their jury sizes for misdemeanor trials. Curiously however, contrary to the predictions of probability theory and "common sense", these reductions in jury sizes have failed to deliver the expected reduction in mistrial rates. In this paper we offer two interrelated explanations for this fact. We formulate a jury model, from which we derive several formal propositions relating to jury deliberation in the presence of informational cascades and heterogeneous jurors. These results inform not only our understanding of jury deliberation, but also democratic theory more broadly.