Liability rules under evidentiary uncertainty

This paper characterizes the efficient evidentiary thresholds for establishing negligence when courts have imperfect evidence about care. An evidentiary threshold refers to the “weight of evidence”, given the risk of error, for ruling that a party was at fault and differs from the substantive due care standard that the party should meet. I show that efficient evidentiary thresholds differ between liability rules and are therefore inconsistent with a general invariant standard of proof. In particular, they require a greater “weight of evidence” than the common law standard of the preponderance of evidence, which tends to induce overcompliance.