Conjunction and Aggregation

This Article begins with the puzzle of why law does not embrace the “product rule”; a mathematically-inclined judge or jury that thought a defendant .6 likely to have been negligent and .7 likely to have caused plaintiff’s harm might conclude that plaintiff had failed to satisfy the preponderance of the evidence standard. Following some discussion of a number of reactions to this puzzle, the Article advances the idea that the process of aggregating multiple jurors’ assessments overlooks valuable information. First, following the Condorcet Jury Theorem, agreement among jurors might raise our level of confidence beyond what the jurors themselves report. Second, a supermajority’s mean or median voter is likely to have a different assessment from that gained from the marginal juror. As such, a supermajority (or unanimity) rule may take the place of the product rule where there are multiple requirements for liability or guilt. An attempt to extract this inframarginal information more directly would likely generate strategic behavior problems. The analysis is extended to panels of judges, for whom outcome voting may (somewhat similarly) substitute for the product rule.