Correlation Equals Causation? Potential Hurdles for Defendants in Daubert Motions against Causation Experts.

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[author: Lauren Jones*]

Kovach v. Wheeling & Lake Erie Ry. Co., No. 3:18-CV-02826-JGC, 2021 WL 3774900 (N.D. Ohio Aug. 25, 2021) encourages defense attorneys to challenge experts with tactics other than Daubert, as the court avoided excluding plaintiff’s causation expert.

Mr. Kovach worked at the Wheeling and Lake Erie Railway Company (“Wheeling”) for twenty-five years. While at Wheeling, Mr. Kovach was exposed to various substances including daily contact with diesel fuel. Just two years after his retirement, Mr. Kovach was diagnosed with non-Hodgkin’s lymphoma; he died shortly thereafter.

Mr. Kovach’s widow brought the action, alleging that Wheeling negligently exposed Mr. Kovach to toxic substances which caused his cancer. Wheeling moved to exclude plaintiff’s causation expert, Dr. Arthur Frank. Dr. Frank opined that Mr. Kovach’s exposure to diesel fuel, kerosene, exhaust, pesticides, and herbicides significantly contributed to Mr. Kovach developing cancer.

The court immediately noted its reluctance to exclude experts, encouraging litigants to instead undermine experts through cross-examination or contrary evidence, among other advocacy tactics. Still, Wheeling sought to exclude Dr. Frank’s opinions on general and specific causation, arguing that Dr. Frank used unreliable sources.

Wheeling argued that Dr. Frank failed to establish general causation because he used sources showing benzene’s correlation with cancer, not that benzene caused cancer. However, experts do not need to rely on research showing direct cause-and-effect relationships—associational sources sufficiently point to general causation. Importantly, the court suggested that it can still exclude experts relying on associations if those experts have other deficiencies, such as failing to review medical records, fact depositions, or available exposure data.

Following Dr. Frank’s conclusion that diesel and kerosene contributed to Mr. Kovach’s cancer, Wheeling argued that Dr. Frank’s sources were inapplicable because they dealt with benzene, not diesel or kerosene. Considering that diesel and kerosene contain benzene, Dr. Frank’s focus on benzene was permissible. Again, the court advised Wheeling to question Dr. Frank’s sources through cross-examination instead of excluding Dr. Frank’s opinion outright.

As for specific causation, Wheeling argued that Dr. Frank should not have solely relied upon a letter from plaintiff’s counsel to craft his opinion; the letter outlined Mr. Kovach’s work responsibilities and chemical exposure. The court recognized that relying only on this letter is insufficient, as the letter contained mere assumptions. Nevertheless, assumptions become facts upon which an expert can rely if the assumptions have independent confirming support in the record. Because of this, the court allowed plaintiff’s testimony to “independent[ly]” confirm the letter from her own counsel.

Mrs. Kovach’s testimony came after Dr. Frank completed his report. Still, her testimony aligned with and “independent[ly]” confirmed the assumptions in her counsel’s letter. These assumptions became facts upon which Dr. Frank’s opinion could rest, even though these facts were confirmed (1) after Dr. Frank completed his report (2) by the plaintiff confirming her counsel’s letter.

Next, Wheeling argued that Dr. Frank could not establish specific causation or a differential diagnosis[1] because he did not know the intensity of Mr. Kovach’s chemical exposure. However, “fair[ness]” dictates that plaintiffs’ experts do not need to quantify exposure to create reliable opinions. Considering that it was impossible to examine Mr. Kovach, his twenty-five years of exposure overcame the need to quantify.

The court ultimately denied Wheeling’s Daubert motion. The Kovach case illuminates how courts avoid excluding experts, instead encouraging persuasive advocacy. For example, the court accepted correlational studies as proof of causation, despite correlation and causation being definitionally distinct. The court permitted the expert to research one component of a multi-component substance. Likewise, the court did not require the expert to quantify exposure. Most interestingly, the court allowed the expert to solely rely on assumptions written by plaintiff’s counsel, later confirmed by plaintiff’s testimony; it is a guiding principle that counsel represents and depends upon plaintiff – one should heed the court’s willingness to bend this principle by considering the words of plaintiff and her counsel as independent. In sum, defense attorneys must be proactive in bolstering these causation arguments or otherwise use different advocacy strategies to contest a plaintiff’s expert.

*(license pending)


[1] A differential diagnosis is “a standard scientific technique of identifying the cause of a medical problem by eliminating the likely causes until the most probable one is isolated.” Hardyman v. Norfolk & W. Ry. Co., 243 F.3d 255, 259 (6th Cir. 2001). The Sixth Circuit requires that a doctor performing a differential diagnosis (1) objectively ascertains, to the extent possible, the nature of the patient’s injury, (2) rules in one or more causes of the injury using a valid methodology, and (3) engages in standard diagnostic techniques by which doctors usually rule out alternative causes to conclude as to which cause is most likely. Best v. Lowe’s Home Centers, Inc., 563 F.3d 171, 178 (6th Cir. 2009) (no need to quantify the level of exposure where expert completed differential diagnosis).

DISCLAIMER: Because of the generality of this update, the information provided herein may not be applicable in all situations and should not be acted upon without specific legal advice based on particular situations.

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