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August 2011

Texas Supreme Court Reaffirms Sufficiency Standards For Establishing Causation Based On Epidemiological Evidence

    The Texas Supreme Court in Merck & Co., Inc. v. Garza, No. 09-0073 (Tex. Aug. 26, 2011) has reaffirmed and clarified the requirements imposed by state law for determining whether epidemiological evidence is sufficient to prove causation.  Applying its seminal decision in Merrell Dow Pharm., Inc. v. Havner, 953 S.W.2d 706 (Tex. 1997), the court held that a plaintiff relying on epidemiological evidence – regardless of whether the studies involved are observational, meta-analyses, or randomized clinical trials – cannot meet her burden of proving general causation without presenting two or more properly-designed studies that show a doubling of the risk in question.  Moreover, the plaintiff must demonstrate that his or her individual circumstances are substantially similar to the subjects in the cited studies and that other plausible causes of the injury or condition are excluded with reasonable certainty.  In Garza, the court found that the plaintiffs had failed to meet these standards and reversed the jury's $32 million product liability verdict, rendering judgment instead for the defendant.

    The plaintiffs in the case had sued Merck, the manufacturer of the prescription drug Vioxx®, claiming that use of the drug caused Leonel Garza's fatal heart attack.  Garza, however, had a long history of heart problems prior to taking Vioxx and only took a limited amount of the drug for a relatively short period before his death.  Merck repeatedly challenged the scientific reliability of plaintiffs' evidence linking Garza's heart attack to Vioxx, but the trial court overruled those objections.  The intermediate court of appeals likewise rejected Merck's argument that the plaintiffs failed to prove causation under Havner because they had not produced two statistically-significant epidemiological studies showing that Vioxx at the dose and for the duration taken by Garza more than doubles the risk of heart attack.  The appellate court concluded that Havner did not establish such a bright-line test and instead held that sufficiency of the causation evidence should be determined from its totality.  The Texas Supreme Court granted Merck's petition for review and reversed.

    In an opinion authored by Justice Hecht, and without dissent, the Texas Supreme Court agreed with Merck that Havner's requirements were fatal to plaintiffs' claims.  It rejected plaintiffs' contention that Havner applied only to the specific type of observational studies at issue in that case, and did not extend to the more reliable, controlled clinical trials relied on by plaintiffs' causation experts.  Furthermore, the Garza court confirmed that Havner imposes a firm requirement demanding at least two studies that establish a doubling of the risk, and that the totality of the evidence only comes into play after a plaintiff meets this initial burden:

Havner holds, and we reiterate, that when parties attempt to prove general causation using epidemiological evidence, a threshold requirement of reliability is that the evidence demonstrate a statistically significant doubling of the risk.  In addition, Havner requires that a plaintiff show "that he or she is similar to [the subjects] in the studies" and that "other plausible causes of the injury or condition that could be negated [are excluded] with reasonable certainty."  Havner also requires that even if the studies meet the threshold requirements of reliability, sound methodology still necessitates that courts examine the design and execution of epidemiological studies using factors like the Bradford-Hill criteria to reveal any biases that might have skewed the results of the study, and to ensure that the standards of reliability are met in at least two properly designed studies.  Thus, a plaintiff must first pass the primary reliability inquiry by meeting Havner's threshold requirements of general causation.  Then, courts must conduct the secondary reliability inquiry that examines the soundness of a study's findings using the totality of the evidence test.

Slip op. at 13-14 (internal footnotes omitted, alterations in original). 

    Applying these standards, the court concluded that the plaintiffs' evidence was insufficient to prove general causation.  For instance, the plaintiffs' reliance on two studies that purportedly showed a doubling of the risk of heart attacks for Vioxx users was misplaced, as the conditions in those studies were not "substantially similar" to those surrounding Garza's Vioxx use.  One study examined patients who used a much higher dose of the drug for a longer duration than Garza, while another involved a meta-analysis that combined a number of different studies, with differing dosages, durations and comparison drugs.  Moreover, the court found that the plaintiffs had presented no reliable basis for extrapolating those studies' results to Garza's drug dosage or duration of use.  Accordingly, the plaintiffs failed to meet their burden of proof and Merck was entitled to judgment as a matter of law.

    Garza is a significant decision for companies defending against claims grounded in Texas law and based on epidemiological evidence that assert a drug caused a particular injury.  The court's opinion makes clear that Havner's sufficiency standard applies regardless of the type of scientific studies relied upon, and that Havner will not permit plaintiffs to satisfy their burden by pointing only to the totality of the causation evidence where they otherwise lack proof of two different, well-designed studies showing a doubling of the risk.   

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