California Trial Court’s Gatekeeping Function Reaffirmed

In 2012, the California Supreme Court firmly established that the trial courts have the duty to act as “gatekeepers” to exclude speculative testimony. In Sargon Enterprises, Inc. v. University of Southern California (2012) 55 Cal.4th 747, the high court reached its holding by relying on California Evidence Code sections 801, subdivision (b), and 802 to establish that “the trial court acts as a gatekeeper to exclude expert opinion testimony that is (1) based on matter of a type on which an expert may not reasonably rely, (2) based on reasons unsupported by the material on which the expert relies, or 3) speculative.” (Id. at pp. 771-772.)

More than a decade later, a recent decision by the California intermediate appellate court reaffirmed the trial court’s gatekeeping role in Onglyza Product Cases (April 19, 2023, A165387) ___ Cal.App.5th ____ (Onglyza). The First Appellate District hears all appellate matters from the following northern California counties: Alameda, Contra Costa, Fresno, Marin, Monterey, San Benito, San Francisco, San Mateo, Santa Clara, and Santa Cruz counties.

At issue in Onglyza was whether the trial court properly excluded the opinions by the plaintiffs’ general causation expert, Dr. Parag Goyal, a cardiologist, who was asked to opine whether saxagliptin was capable of causing heart failure. The case was a coordinated judicial proceeding (similar to multidistrict litigation cases at the federal level) consisting of 13 cases brought by plaintiffs who alleged injuries after taking drugs with saxagliptin (the main ingredient found in two medications to treat type 2 diabetes).

Dr. Goyal opined that saxagliptin was capable of causing heart failure by relying on a single study known as SAVOR – a randomized, double-blind, placebo-controlled study that consisted of 16,492 patients with type 2 diabetes who were at high risk of cardiovascular disease. SAVOR concluded that saxagliptin did not increase or decrease the risk of cardiovascular death, myocardial infarction, or ischemic stroke. However, SAVOR noted a statistically significant[1] finding of hospitalization for heart failure. The study’s authors noted that this finding “was unexpected and should be considered within the context of multiple testing that may have resulted in a false positive result.” The authors further cautioned that the finding “merits further investigation and needs to be confirmed in other ongoing studies, and a class effect should not be presumed.”

Despite the authors’ cautionary warnings, Dr. Goyal concluded that “the finding from SAVOR alone showed a causal link between saxagliptin and heart failure.” The trial court found that Dr. Goyal could not reasonably rely on a single study as “ ‘[r]arely, if ever, does a single study persuasively demonstrate a cause-effect relationship. It is important that a study be replicated in different populations and by different investigators before a causal relationship is accepted by epidemiologists and other scientists.’ ”

Furthermore, the Court of Appeal questioned the methodology performed by Dr. Goyal in reaching his opinions. Although Dr. Goyal employed the Bradford Hill analysis, an accepted methodology consisting of 9 factors to help determine if observed epidemiologic associations are causal, the Court of Appeal agreed with the trial court’s finding that Dr. Goyal misapplied 6 of the 9 factors, thereby upsetting the ultimate opinion on causation. The Court of Appeal held that “[t]his was a proper exercise of the court’s gatekeeping responsibility.” For example, “strength of association” is one factor that examines how strong the association is between the exposure and the disease. The higher the risk, the greater the likelihood the relationship is causal. Based on the SAVOR’s finding that the hazard ratio for hospitalization for increased heart failure was 1.27, Dr. Goyal opined that SAVOR was a reliable study for assessing strength. However, Dr. Goyal was unable to state whether 1.27 was a strong or weak association. The trial court therefore found that Dr. Goyal did not opine on the “strength of association factor.”

The Court of Appeal did not agree with the argument that the trial court was impermissibly weighing the probative value of Dr. Goyal’s opinions. Rather, the Court of Appeal found that that trial court properly considered whether Dr. Goyal’s methodology was reliable when it excluded his opinions on general causation.

Although the trial court’s role as gatekeeper in excluding speculative expert opinion was firmly established over a decade ago, the Onglyza opinion lends further support to trial judges to ensure that expert opinions are based on scientifically reliable methodologies.