Empirical Comparisons of the Contributory versus Comparative Negligence Rules

The liability rule traditionally used in accident law when both the injurer’s and the victim’s behaviour affect the likelihood of an accident occurring is the rule of contributory negligence. Under it, the injurer is liable for the full amount of the victim’s damage only if the injurer’s behavior is negligent and the victim’s behavior is non-negligent. If both parties are negligent, only the victim is negligent, or neither party is negligent, then the injurer is not liable for any amount of damage. However in many jurisdictions the contributory negligence rule has been replaced by the comparative negligence rule. The new rule differs from the old in that the injurer and the victim share liability for the victim’s damage when both parties are negligent, where under the usual sharing formula the injurer pays a proportion of the victim’s damage equal to the injurer’s fault relative to the total fault of both parties. When either the injurer or the victim is negligent or neither party is negligent, the two rules are the same. Thirty-eight American states shifted from contributory negligence to comparative negligence between 1969 and 1984 and, as of 1985, only five states still used the older rule (Flanigan et al 1989). The comparative negligence rule is also used in the United Kingdom, France, Germany, Russia, and in maritime law. (See Curran 1992 for an empirical study explaining the spread of the comparative negligence rule in the U.S.) What guidance does theory provide for empirical testing of the effects of liability rules? The traditional theoretical analysis of the contributory and the comparative negligence rules argues that both rules give injurers and victims incentives to take economically efficient levels of care (see Shavell 1987). The basic argument is the same for both rules and relies on the fact that injurers and victims both receive large, discontinuous cost reductions when they increase their care levels just enough to be found non-negligent if an accident occurs: injurers because they avoid liability for all or a share of victims’ damages and victims because they cannot collect from injurers for their damages when they are negligent. These large cost reductions give both injurers and victims an incentive to use