Calculating A Fair Trial

Dana Mackenzie does the math to determine the ideal size and design of a jury:

In a very provocative 1992 paper, George Thomas, a law professor at Rutgers University, and his student Barry Pollack, now a partner at Pollack Solomon Duffy LLP in Boston, argued that the function of a jury is to serve as a proxy for society. In ancient Greece every citizen of the polis served on the jury. In the modern world this is impractical, so we settle for juries of 12. …

If you pick 12 people at random, how likely is it that they will disagree unanimously with the majority of society? Not very likely. How likely is it that they will disagree with society by a 9-to-3 majority? Thomas and Pollack crunched the numbers, and Suzuki recrunched them. And they found a surprising consistency. For every margin that the Supreme Court has allowed to stand (6- to 0, 10 to 2, 9 to 3), the probability of a disagreement between society and the jury is less than 1.5 percent. And for every margin that the Supreme Court has ruled unconstitutional (5 to 1, 5 to 0), the probability of disagreement is greater than 1.5 percent. Thus, without realizing it, the Supreme Court has consistently held that there should be less than a 1-60 chance that the jury will disagree with society. Judicial hunch meets mathematical rigor!