Judges as Gatekeepers: Requiring a "Plain English" Explanation of Expert Testimony and Meaningful Analysis of an Expert's "Principles and Methods"

The Seventh Circuit recently made clear that a district court’s duty to rule on the admissibility of expert testimony requires a meaningful examination into whether a proffered expert’s analysis is methodologically sound. After reversing the plaintiff’s jury verdict as legally deficient, the court in ATA Airlines, Inc. v. Federal Express Corp. addressed the jury’s damages award, ruling that it was based on a fundamentally flawed regression analysis. 

The district court had allowed plaintiff’s expert, a forensic accountant, to present damages testimony based on a regression analysis, reasoning in part that “regression analysis is accepted, so this is not ‘junk science.’” The district court ruled that the defendant’s objections about how the expert constructed his regression analysis could be explored on cross-examination. But the jury accepted the expert’s testimony, awarding every penny he proposed as plaintiff’s damages.

The court of appeals concluded that the district court did not do enough to ensure that the expert’s testimony complied with Federal Rules of Evidence 702(2) & (3). Underscoring the need to conduct a detailed analysis of an expert’s method and its proposed application, Judge Posner devoted 13 pages to discussing the basics of regression analysis, including suggesting several sources as background reading, and various flaws in the expert’s approach. As the decision states, the court went “on at such length about the deficiencies of the regression analysis in order to remind district judges that, painful as it may be, it is their responsibility to screen expert testimony, however technical.” The decision concludes that the expert’s method was so flawed as to result in a complete absence of damages proof. 

The court of appeals also emphasized, as it has in the past, that a district judge may appoint its own expert under Fed. R. Evid. 706 to assist it in evaluating the parties’ proposed expert testimony. But, most strikingly, the court highlights the responsibility of the parties to explain the proffered expert testimony “in plain English,” suggesting that a lawyer’s inability to give that explanation is grounds enough for excluding an expert’s testimony: “If a party’s lawyer cannot understand the testimony of the party’s own expert, the testimony should be withheld from the jury. Evidence unintelligible to the trier or triers of fact has no place in a trial.”