Private Law Theory

ABSTRACT
In an important category of medical negligence cases, such as cases of doctors negligently failing to diagnose a potentially fatal disease, the defendant significantly increases the risk of harm to the plaintiff, but that increase in risk is insufficient to satisfy the preponderance test of factual causation, which requires proof that but for the defendant’s negligence, the plaintiff would not have suffered harm. For example, suppose a doctor’s negligently delayed diagnosis of cancer increased the risk of death to the patient from 30% (if the doctor had not been negligent) to 45%, and there is no feasible way to determine whether the patient is within the group who would have died apart from that negligence or within the group who died because of the negligence. If the patient dies of cancer, the preponderance test of causation cannot be satisfied, because the doctor’s negligence only increased the risk of death by 15%, and the patient is more likely to be in the 30% group of patients who would have died apart from that negligence.

Most courts that have addressed this issue have permitted partial damages in these cases. I agree with this result. But I disagree with the ‘subtraction’ computation method that courts almost uniformly employ. In the example, they would award 15% of the damages that the plaintiff’s estate would ordinarily receive if the plaintiff had been negligently killed in a fact pattern satisfying the preponderance test. In my view, the estate should receive 33% of ordinary damages, not 15%, because the chance that the doctor’s negligence caused the death is more accurately computed by the ratio 15/45. The subtraction method, as compared to the ratio method, undercompensates plaintiffs …

Kenneth W Simons, Lost Chance of a Better Medical Outcome: New Tort, New Type of Compensable Injury, or New Causation Rule?, 73 DePaul Law Review 547 (2024).