Ninth Circuit Reemphasizes That Challenges to Expert Credibility and the Strength of a Particular Scientific Method Best Left for Jury

The Ninth Circuit reversed a district court’s exclusion of expert testimony in a water contamination case that is instructive for expert challenges in any safety-related case.  The City of Pomona, California filed suit against the company that imported sodium nitrate into the United States from 1927 through the 1950s from Chile’s Atacama Desert on the grounds that the fertilizer containing this chemical was the most likely dominant source of alleged perchlorate contamination in the city’s water supply.

The city’s expert witness on causation relied on a “stable isotope analysis.”  The district court excluded the witness’s testimony because his opinions were subject to ongoing future methodological revisions and not yet certified, his procedures were not subject to retesting, and the reference database he used to link the alleged contamination to Chile’s Atacama Desert was too small.  The parties agreed to a conditional dismissal with prejudice to facilitate review of the exclusion order.

The Ninth Circuit reversed, finding that the existence of ongoing research does not necessarily invalidate the reliability of expert testimony.  The methodology relied on by the city’s expert was the product of 12 peer-reviewed publications and inter-laboratory collaboration, and even though the standard was subject to some disagreement, it was not “the product of a hasty, incomplete effort.”  The Ninth Circuit found the weight the district court gave to the lack of EPA certification of the isotopic analysis of perchlorate performed by the expert was an abuse of discretion; the Federal Rules of Evidence did not require an endorsement of the methodology from the EPA.  With respect to the expert’s testing, the fact he did not independently verify his test results with a lab other than his own goes to the weight of his testimony, not the admissibility.  Similarly, challenges to whether an expert followed certain protocols are typically issues for the jury in assessing the weight of the expert’s conclusions.  Lastly, the Ninth Circuit emphasized that even if the expert’s conclusions were “shaky,” they should be attacked by “cross examination, contrary evidence, and attention to the burden of proof, not exclusion.”