Choosing the right expert witness is an integral part of counsel's strategy when litigating any case. A party generally retains an expert to help bolster a key element of its claim or defense and to assist the judge or jury to better understand a complex issue. The use of expert opinion testimony is pointless, however, if the expert's opinion is inadmissible.

To be admissible, expert testimony must rest both "on a reliable foundation" and be "relevant to the task at hand" (Daubert v. Merrell Dow Pharm., Inc., 509 U.S. 579, 580 (1993)). Often, counsel chooses to attack the types of data the expert relied on to question the reliability of the expert opinion's methodology. Courts must then examine whether the data relied on, or ignored by, the expert witness goes to the reliability of the expert's methodology or the weight of the expert's opinion. As shown by two recently issued opinions, this conclusion is important as it may determine whether an expert's testimony is admitted or excluded by the court.

In Hughes v. Kia Motors Corp., the US Court of Appeals for the Eleventh Circuit affirmed the district court's decision to exclude the testimony of the plaintiff's causation expert witness (No. 13-10922, , at *1 (Sept. 12, 2014)). In this case, the plaintiff sued the defendant, an automobile manufacturer, alleging that a design defect in the car owned by the plaintiff's daughter led to her death after a car accident (Hughes, , at *2).

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. Additionally, 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. (Hughes, , at *10.)

In contrast, the US Court of Appeals for the Tenth Circuit, in In re: Urethane Antitrust Litigation, affirmed the district court's order admitting the plaintiffs' expert testimony over the defendant's challenge to the reliability of the expert's methodology (No. 13-3215, , at *14 (10th Cir. Sept. 29, 2014)). The appellant argued that the plaintiffs' expert's testimony was unreliable because the expert manufactured his opinion through "variable shopping" (choosing variables for his analysis to generate supra-competitive prices) and "benchmark shopping" (moving the conspiracy period to a benchmark period to manufacture supra-competitive prices during the conspiracy period) (In re: Urethane Antitrust Litig., , at *12).

In affirming the district court's decision, 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 re: Urethane Antitrust Litig., , at *14.)

As shown by both 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 should ensure that the expert's methodology is clearly explained and 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.

Practical Law has a variety of resources to help counsel retain an expert witness and effectively use expert witnesses in litigation, including: