Not all scientific evidence is created equal.  The “Hierarchy of Scientific Evidence” pyramid (you know the one – multi-colored, with case reports at the bottom and randomized controlled trials at the top) is your friend.  Learn it, love it, and use it all the time.  Understanding the limitations of the scientific evidence on which plaintiff’s causation expert bases his opinion is critical to the defense of any product liability case.

To successfully argue to exclude an expert or effectively cross examine him at trial, a good defense lawyer must carefully analyze the details of the studies upon which her opponent relies.  Who funded the study?  What kind of a study was it – case report or placebo controlled?  How many people participated?  What was the dose or level of exposure?  The key is to uncover and expose all the ways in which plaintiff’s scientific evidence is based on facts contrary to those in your case (i.e., dose, duration, etc.).  If a study is sufficiently factually divorced from plaintiff’s allegations, any expert opinion premised on that study may be excluded as unreliable.  The Fifth Circuit engaged in that very analysis last week when it affirmed a Texas district court’s exclusion of two expert reports for failing to meet the requirements of Federal Rule of Evidence 702.

The case – Macy v. Whirlpool Corp., App. No. 14-20603, 2015 WL 3505511 (5th Cir. Jun. 4, 2015) – was brought by two homeowners alleging personal injuries from a low-level carbon monoxide leak from their kitchen stove.  In support of their claims, the plaintiffs submitted a general and specific causation report from Dr. Penney, a medical doctor.  He opined that low-level exposure to carbon monoxide could cause the types of injuries of which the plaintiffs complained and that plaintiffs’ alleged injuries were in fact caused by exposure to carbon monoxide from the gas stove.  In furtherance of its responsibility to act as a gatekeeper to prevent the jury from considering unreliable expert testimony, the district court rejected the reports and granted summary judgment in Whirlpool’s favor. On appeal, the Fifth Circuit agreed.

The Fifth Circuit began by analyzing whether the proffered expert testimony was relevant and reliable.  The court performed an exacting review of the scientific literature on which the doctor premised his general causation opinion.  The analysis is instructive as it identifies many of the same questions defense lawyers must ask for the purpose of drafting dispositive briefs and preparing for cross examinations.

The Fifth Circuit concluded that certain of the studies on which Dr. Penney relied did not assess the relationship between low-level carbon monoxide exposure and the injuries alleged by the plaintiffs.  Rather, the studies examined injuries caused by significantly higher levels of carbon monoxide.  Relying on this discrepancy, the Fifth Circuit concluded that the premise of Dr. Penny’s opinion was not relevant to the causation question before the trial court.

The Fifth Circuit made clear not to suggest that an expert must support his opinion with published studies that “unequivocally support his conclusion, but rather his testimony “must be reliable at every step, including the methodology employed, the facts underlying the expert’s opinion, and the link between the facts and the conclusion.” Whirlpool, at *3.  Because the factual premise of the studies was inconsistent with the alleged factual premise of the plaintiffs’ injuries, the 5th Circuit affirmed the trial court’s conclusion that the plaintiffs’ causation evidence did not meet the reliability requirements of Federal Rule 702.  On this basis, the Fifth Circuit confirmed the trial court’s exclusion of the report and affirmed the grant of summary judgment in Whirlpool’s favor.

A close and careful look at the scientific evidence on which the plaintiff’s expert based his general causation opinion revealed that the studies had nothing to do with the facts of the case and an expert opinion based on the same was unreliable.  As illustrated by the Fifth Circuit’s Whirlpool opinion, a deep dive into the scientific evidence on which plaintiff’s experts rely is critical to the successful defense of a products case.