Notably, the expert's methodology and qualifications were stipulated to and unquestioned by the court. Instead the trial court ruled his ultimate conclusions were “speculative” and contradicted by eyewitnesses. The District Court excluded the testimony based upon a lack of “sufficient facts or data” under rule 702 of Evidence. The exclusion of this evidence eliminated plaintiffs' causation evidence and  summary judgment was granted by the United States District Court for the District of Idaho. The United States Court of Appeals, Ninth Circuit reversed.

While the trial court serves as a “gatekeeper” she does not serve as a “fact-finder.” The trial court  may screen expert testimony for reliability and to assure it is not speculative but it is not to make factual determinations or weigh the evidence in so doing. Daubert v. Merrell Dow Pharm., Inc., 509 U.S. 579, 586 (1993) places the focus of this inquiry on the expert's methodology not his or her conclusion or opinions.  

Ultimately, “the test under Daubert is not the correctness of the expert's conclusions but the soundness of his methodology.” Daubert II, 43 F.3d at 1318. The court is “a gatekeeper, not a fact finder.”  Accordingly, “[t]he district court is not tasked with deciding whether the expert is right or wrong, just whether his testimony has substance such that it would be helpful to a jury.” Alaska Rent-A-Car, Inc., 738 F.3d at 969–70. If the proposed testimony meets the thresholds of relevance and reliability, its proponent is “entitled to have the jury decide upon [its] credibility, rather than the judge.”