Earlier this month, the Ninth Circuit affirmed a California district court’s orders excluding two expert witnesses for failure to prove specific causation, and granting defendant’s motion for summary judgment. The decision affirms the continued importance of expert witness opinions in allowing—or preventing—a plaintiff’s cause of action to proceed to trial. The case is Nelson v. Matrixx Initiatives, Inc., No. 12-17455, 2015 WL 412858 (9th Cir. Feb. 2, 2015).

Under California law, to plead a successful cause of action in a toxic tort case, a plaintiff must show both general and specific causation. General causation demonstrates that the substance at issue was capable of causing the injury alleged, whereas specific causation requires a showing that the substances caused, or was a substantial factor in causing, the specific plaintiff’s injury. In most cases, plaintiffs are required to offer expert testimony regarding both types of causation.

In Nelson, the plaintiff sought to introduce expert testimony to establish the causation element of his claim for anosmia (loss of smell) against the companies that manufacture and market a homeopathic nasal product. At issue on summary judgment was whether plaintiff adequately alleged specific causation. The experts engaged in differential diagnosis, which is “the determination of which of two or more diseases with similar symptoms is the one from which the patient is suffering, by a systematic comparison and contrasting of the clinical findings.” Clausen v. M/V New Carissa, 339 F.3d 1049, 1057 (citing Stedman’s Medical Dictionary 474 (26th ed. 1995)). First, the expert must rule in a list of potential causes of the injury. Then, the expert must eliminate—or rule out—the identified potential causes, providing “reasons for rejecting alternative hypotheses using scientific methods and procedures and the elimination of those hypotheses must be founded on more than subjective beliefs or unsupported speculation.” Id. at 1058. The District Court held that the experts’ testimony was inadmissible because they were not based on reliable methods as required under Daubert. In particular, the court found that the experts’ opinions failed to explain sufficiently the scientific method for ruling in the nasal spray at issue and excluding potential alternative causes for smell loss, such as age or the cold virus. The Ninth Circuit affirmed, holding that the district court did not abuse its discretion as to the question of reliability on specific causation or exclusion of both experts on that basis.

Nelson reminds us that although plaintiffs need not offer data on the precise degree of chemical exposure suffered, the specific causation inquiry requires reliable expert testimony based on more than mere speculation or unsupported opinion. Thus, the fundamental rule of tort actions remains unbroken: claims face dismissal if the element of causation is not established adequately after applying Daubert, especially in the context of plaintiffs alleging personal injury from toxic substances.

Earlier this month, the Ninth Circuit affirmed a California district court’s orders excluding two expert witnesses for failure to prove specific causation, and granting defendant’s motion for summary judgment. The decision affirms the continued importance of expert witness opinions in allowing—or preventing—a plaintiff’s cause of action to proceed to trial. The case is Nelson v. Matrixx Initiatives, Inc., No. 12-17455, 2015 WL 412858 (9th Cir. Feb. 2, 2015).

Under California law, to plead a successful cause of action in a toxic tort case, a plaintiff must show both general and specific causation. General causation demonstrates that the substance at issue was capable of causing the injury alleged, whereas specific causation requires a showing that the substances caused, or was a substantial factor in causing, the specific plaintiff’s injury. In most cases, plaintiffs are required to offer expert testimony regarding both types of causation.

In Nelson, the plaintiff sought to introduce expert testimony to establish the causation element of his claim for anosmia (loss of smell) against the companies that manufacture and market a homeopathic nasal product. At issue on summary judgment was whether plaintiff adequately alleged specific causation. The experts engaged in differential diagnosis, which is “the determination of which of two or more diseases with similar symptoms is the one from which the patient is suffering, by a systematic comparison and contrasting of the clinical findings.” Clausen v. M/V New Carissa, 339 F.3d 1049, 1057 (citing Stedman’s Medical Dictionary 474 (26th ed. 1995)). First, the expert must rule in a list of potential causes of the injury. Then, the expert must eliminate—or rule out—the identified potential causes, providing “reasons for rejecting alternative hypotheses using scientific methods and procedures and the elimination of those hypotheses must be founded on more than subjective beliefs or unsupported speculation.” Id. at 1058. The District Court held that the experts’ testimony was inadmissible because they were not based on reliable methods as required under Daubert. In particular, the court found that the experts’ opinions failed to explain sufficiently the scientific method for ruling in the nasal spray at issue and excluding potential alternative causes for smell loss, such as age or the cold virus. The Ninth Circuit affirmed, holding that the district court did not abuse its discretion as to the question of reliability on specific causation or exclusion of both experts on that basis.

Nelson reminds us that although plaintiffs need not offer data on the precise degree of chemical exposure suffered, the specific causation inquiry requires reliable expert testimony based on more than mere speculation or unsupported opinion. Thus, the fundamental rule of tort actions remains unbroken: claims face dismissal if the element of causation is not established adequately after applying Daubert, especially in the context of plaintiffs alleging personal injury from toxic substances.