Texas Supreme Court Imposes Strict Standards Governing Use Of Epidemiological Evidence In Proving Causation

Previously published on September 7, 2011.

Keywords: Product liability, causation, Havner, Vioxx, totality of evidence

The Texas Supreme Court recently held that plaintiffs seeking to prove general causation with epidemiological evidence must produce two independent studies demonstrating that subjects who used the product at issue under circumstances substantially similar to those encountered by the plaintiff doubled their the risk of injury. Merck & Co. v. Garza, 2011 WL 3796364 (Tex. Aug. 26, 2011).

Leonel Garza, a 71-year old with a 20-year history of heart disease, died of a heart attack less than one month after he began taking the anti-inflammatory drug Vioxx. Garza's family sued Merck, the manufacturer of Vioxx, alleging defective design and inadequate warnings. A jury awarded the Garzas $7 million in actual damages and $25 million in punitive damages (reduced to $750,000).

The court of appeals held that plaintiffs introduced sufficient evidence that Vioxx caused Garza's death, rejecting Merck's argument that plaintiffs' causation evidence was inadequate under the standard adopted in Merrell Dow Pharmaceuticals, Inc. v. Havner, 953 S.W.2d 706 (Tex. 1997). In Havner, the Texas Supreme Court held that a causation opinion based on epidemiological evidence must be supported by statistically-significant studies showing a "doubling of the risk" of injury at a comparable dose and duration to that experienced by the plaintiff. The Havner court observed, however, that "a relative risk of more than 2.0" is not a "litmus test" and that trial judges should consider the "totality of the evidence." Citing this "totality of the evidence" standard, the court of appeals in Garza held that Havner did not establish a "bright-line test."

The Texas Supreme Court reversed, holding that when plaintiffs "attempt to prove general causation using epidemiological evidence," plaintiffs must produce two independent studies finding "a statistically significant doubling of the risk" of injury for patients taking the drug, show that plaintiffs are "similar to the subjects in the studies" in terms of dosage and duration, and demonstrate that "other plausible causes of the injury or condition that could be negated are excluded with reasonable certainty." The court stated that only if plaintiffs satisfy these "threshold requirements" must the trial judge "examine[] the soundness" of the studies under a "totality of the evidence" standard.

In so holding, the Texas...