Expert opinion neglecting alternative hypotheses of causation may be excluded: Ninth Circuit

The Ninth Circuit recently upheld the decision of a district court in California which excluded the testimony of two expert witnesses in a toxic tort case. The testimonies had been excluded on the ground that the opinions were not “sufficiently reliable” on the issue of specific causation. The Ninth Circuit, in Michael D. Nelson v. Matrixx Initiatives, Inc. and Zicam, LLC , agreed with the finding of the U.S. District Court for the Northern District of California that the expert testimony and report failed to provide a reliable method for establishing a necessary causal relationship between the pharmaceutical product, Zicam, and the plaintiff’s loss of smell.

The issue arose out of a suit instituted by Mr. Micheal D. Nelson, a lawyer, alleging a loss of sense of smell and taste as a result of his use of Zicam Cold Remedy Nasal Gel swabs and spray, a homeopathic cold remedy, which is manufactured and marketed by the defendants. In the operative complaint, the plaintiff alleged claims of manufacturing defect, design defect, failure to warn, intentional misrepresentation and false promise, fraudulent concealment, and negligence.

The District Court earlier held that the testimony of Drs. Peter Davis and Greg Hwang failed to rule out the factors of age and cold virus, which are “well-established, common causes of smell loss”, in connection with Mr. Nelson’s grievance. Hearing Mr. Nelson’s appeal from this decision, Circuit Judges Wallace, Smith and Friedland approved the above view and observed, citing a 2003 Ninth Circuit opinion in the case Clausen v. M/V New Carissa (339 F.3d 1049), that although differential diagnosis is admissible under Daubert, “expert testimony that neglects to consider a hypothesis that might explain the clinical findings under consideration may also be unreliable”. Without reasonable grounds for eliminating alternative potential causes, any opinion attributing specific causation to Zicam would be based on little more than “subjective beliefs or unsupported speculation” of the experts, and thus liable to be excluded, added the Court, quoting from Claar v. Burlington N.R.R. Co. (29 F.3d 499).