Malfunction theory allows plaintiffs in a products liability case to prove the probability of a defect by eliminating normal causes of malfunctions, even without proving the specific existence of a product defect. Plaintiffs have applied malfunction theory to devastating effect on the defense of a products liability case, which is already a plaintiff-friendly environment. Courts throughout the nation are utilizing and developing malfunction theory to relax, or even excuse proof of defect and causation in products liability cases. This article argues that malfunction theory poses a triple threat to defendants by: (i) removing the requirement that plaintiffs prove a specific product defect; (ii) relaxing the causation requirements that plaintiffs must show; and (iii) potentially allowing plaintiffs' experts to provide otherwise impermissibly unsupported opinions. However, at least one recent case provides the possibility that unsupported expert testimony presents the Achilles heel to this otherwise unbounded theory.
I. Plaintiff-friendly Product Liability Law
Product liability law essentially undid previous common law. Most notably, product liability law created a dangerous environment for any person operating in the stream of commerce by allowing claims against any defendant in the stream of commerce relative to the product with no privity requirement and without proof of fault. Courts also did away with the traditional requirement of proving fault, or negligence-allowing strict liability against any product seller. When neither privity of contract nor negligence is required, the burden often effectively shifts to defendants to figure out who is responsible for the harm allegedly caused to a plaintiff.
Ordinarily in product liability cases in most jurisdictions, a plaintiff must prove that: a product was in a defective condition unreasonably dangerous to the consumer, the defect caused the injury, the defect existed at the time of sale, and the product was expected to and did reach the consumer without substantial change in condition.2
The application of the malfunction theory to this already plaintiff-oriented body of law has the potential to expose defendants in the stream of commerce even further.
Malfunction theory is being expanded in most jurisdictions, some in a very relaxed manner, to provide alternate ways in which plaintiffs may successfully bring a products liability case despite the lack of direct evidence of defect and/or causation due to factors such as destruction or loss of the product in question. Under varying circumstances in different jurisdictions, courts are permitting circumstantial evidence as the basis for a prima facie products liability case in the absence of direct evidence of defect, causation, or both.
II. Malfunction Theory Basics
A plaintiff in a product liability action may be able to establish a prima facie case by providing evidence of the nature of a product's malfunction under circumstances that give rise to an inference that the malfunction would not have occurred absent a defect existing at the time of sale. Product liability cases may arise out of a product malfunction that damages or completely destroys a product that is the basis of the products liability case.3 As a result, plaintiff would not be able to produce direct evidence of a specific defect. The malfunction theory essentially allows a plaintiff to present circumstantial evidence of a defect or evidence of an unspecified dangerous condition when direct evidence is unavailable or there is insufficient evidence to identify the specific defect. Additionally, application of the malfunction theory allows the plaintiff to present circumstantial evidence that rules out reasonable secondary causes in lieu of direct evidence of causation.
Given that the malfunction theory implicates permissible inferences for a fact-finder absent direct evidence, the theory essentially operates as a rule …