In some circumstances, a plaintiff lacking direct evidence of an identifiable, specific defect may be permitted to use circumstantial evidence to prove that a product malfunctioned and create a triable inference of a product defect. Some courts may treat proof of a product malfunction as circumstantial evidence of a product defect because a product will not ordinarily malfunction (or perform outside the reasonable safety expectation of the consumer) in the absence of a defect. This circumstantial evidence doctrine, commonly known as the “malfunction theory,” may provide plaintiffs with a pathway to establish a prima facie case of a product defect.
While the malfunction theory sometimes allows plaintiffs to bring a claim for a product defect where the product is no longer available or a specific defect cannot be identified, plaintiffs often attempt to stretch the theory beyond its logical bounds. In a recent case from Idaho, Black v. DJO Global, Inc., the Idaho Supreme Court rejected use of the malfunction theory when the alleged product “failure” (or malfunction) was the occurrence of a known risk, i.e., one that could occur even when the product performs as intended. Black v. DJO Glob., Inc., 488 P.3d 1283, 1288 (Idaho 2021).