When we talk about the scientific method we are really talking about methodology. Below is what the courts are presently using to consider if an expert will be allowed to testify.

Faced with a proffer of expert scientific testimony, then, the trial judge must determine at the outset, pursuant to Rule 104(a), whether the expert is proposing to testify as to (1) scientific knowledge that (2) will assist the trier of fact to understand or determine a fact in issue. This entails a preliminary assessment of whether the reasoning or methodology properly can be applied to the facts in issue. We are confident that federal judges possess the capacity to undertake this review. 5

The challenge we all are concerned about as to being able to testify starts with Daubert. Daubert and the cases following it all relate to the methodology used by the investigator. We have come to believe is we say we used the scientific method we will be in good shape. The problems are, just saying one used the scientific method is not sufficient to pass the test of one testimony being accepted. Although often vital to establishing a claim or defense in federal court, expert testimony only impacts a case if it is admissible. The reliability of the expert's methodology is one of the main factors a court evaluates when determining the admissibility of expert testimony. Two recent federal appellate opinions provide guidance on the factor’s courts consider when making this determination.

In 2014 there was the case of Hughes v. Kia Motors. The Eleventh Circuit held that the plaintiff's expert testimony was inadmissible because the expert witness's methodology was unreliable. Although he stated he had used the scientific method to reach his conclusion, the plaintiff's expert did not specify how the scientific method helped him to reach his conclusions on causation. This was bad enough but in his deposition, the expert stated that he would need to consider a variety of physical factors at the time of the accident in question to properly determine causation, but admitted that he had not considered one factor which may have indicated the decedent's injuries were caused by the initial impact, rather than subsequent impacts as alleged by the plaintiff. The court found that this exclusion, combined with his vague description of the methodology he used to reach his opinion, demonstrated a failure in the expert's methodology. Therefore, because the expert's methodology was unreliable, the court held that the district court properly excluded the expert's testimony and affirmed the court's grant of summary judgment to the defendant.

In another case that same year the Tenth Circuit found that there was no obvious error in the variables chosen by the plaintiffs' expert when formulating his methodology. Instead, the Tenth Circuit found that the appellant's challenge to the data relied on by the plaintiffs' expert concerned the quality of the data, rather than the reliability of the expert's methodology. A challenge to the quality of data used by an expert goes to the weight of the expert's testimony, a question properly submitted to the jury by the district court. Finding that the district court reasonably held that the expert's methodology was reasonable, the Tenth Circuit affirmed the district court's admission of the plaintiffs' expert testimony into evidence.

In 2020 a District Court held a Daubert hearing that lasted three days and featured testimony by 19 general causation witnesses — 7 for the plaintiffs and 12 for Bayer. On October 24, 2018, the District Court entered a detailed 156-page opinion granting Bayer’s Daubert motion as to all the plaintiffs’ experts and denying as moot plaintiffs’ motion to preclude Bayer’s experts.

In this case, he Second Circuit explained that, although an expert need not back his or her opinion with published studies that support his or her conclusion if he or she has used reliable scientific methods to reach that conclusion, the District Court had found that the plaintiffs’ experts did not use reliable scientific methods. Because their conclusions also were not supported by other studies, the experts’ testimony was properly excluded. The Second Circuit emphasized and concluded that the District Court “appropriately undertook a rigorous review” of the experts’ opinions, methodologies, and conclusions, and reasonably found that their methodologies were not sufficiently reliable, and their conclusions were not otherwise supported by the scientific community.

As shown by the opinions, the reliability of an expert's methodology is an important factor considered by courts when determining the admissibility of expert testimony. When seeking to admit expert testimony into evidence, counsel it is important that the expert's methodology can be clearly explained, and it relies on relevant data. Otherwise, there may be a risk that a court will exclude the expert's testimony based on the unreliability of the expert's methodology.

Jim Mazerat
Forensic Investigations Group