Marginal Causation and Injurer Shirking

Abstract

Is the negligence cause-in-fact doctrine efficient? The traditional test has come under increasing criticism by economists and others. Some have suggested switching from the time-honored “but-for” test to “proportional liability,” or “proportional causation,” would advance both efficiency and fairness. The traditional but-for test requires that the plaintiff show that it was more likely than not that the defendant’s untaken precaution, when viewed ex post, would have prevented the plaintiff’s injury. Proportional causation also posits some untaken precaution that was a breach of duty by the defendant. The doctrine then asks the trier of fact to estimate the probability by which the untaken precaution would have prevented the injury. In the most commonly discussed version the plaintiff then recovers his or her actual damages deflated by the “percentage of effectiveness” estimated by the jury or other trier of fact. In comparison to proportional causation, the traditional but-for test is sometimes called “the all-or-nothing rule” because it awards full damages or nothing at all, whereas the proportional rule awards some damages in all cases in which the other elements of negligence are satisfied. This Essay argues that these two causation rules are both currently applied in different situations and are complements in reducing the social costs of accidents.