The Ninth Circuit has not been great for us on Daubert. I suppose it is more accurate to say that the Ninth Circuit has not been great for those who oppose the introduction of unreliable scientific expert opinions. But that is usually us, the defendants resisting plaintiffs' efforts to get to juries with scientific theories that are nothing more than that—theories, or sometimes worse. In 2014, we saw the district court in Merrick v. Novartis correctly exclude a causation expert who could not say whether the drug caused the plaintiff's alleged injury, only to have the Ninth Circuit reverse on the basis that "the relevancy bar is low" for expert opinion. Then we had Wendell v. GlaxoSmithKline, where the district court excluded causation opinions from experts who could not identify a single study showing a causal link, only to again have the Ninth Circuit go on an unwarranted rescue mission.

We were therefore encouraged to see a district court in California cite the above-referenced clunkers, yet still enter a well-reasoned and eminently justified order excluding the plaintiffs' causation experts in the Viagra/Cialis MDL. See In re Viagra and Cialis Prods. Liab. Litig., No. 16-md-02691 (N.D. Cal. Jan. 13, 2020). The plaintiffs alleged that use of prescription drugs known as PDE5 inhibitors caused or exacerbated their melanoma, which is the most serious form of skin cancer. Whether these products could cause melanoma, however, was hotly contested, mainly because of a single 2014 article reporting an association, but cautioning that its findings were insufficient to alter clinical recommendations and acknowledging a need for further investigation. Id. at *1. Multiple other articles and abstracts followed, but none concluded that the products caused melanoma progression or even that there was a particularly strong association. Id. at *3.

After four days of hearings, the MDL judge granted the defendants' motion to exclude all of the plaintiffs' general causation experts. That is to say, the plaintiffs have no admissible expert opinions that use of PDE5 inhibitors can cause melanoma progression, which is a big deal.

How did the judge get there? Well, the plaintiffs had three general causation experts who relied on the articles mentioned above and analysis under the Bradford Hill criteria for assessing causation. Those criteria are: (1) the strength of the association, (2) consistency, (3) specificity, (4) temporality, (5) biological gradient of dose response, (6) biological plausibility, (7) coherence, (8) experimental evidence, and (9) analogy. Id. at *8. We do not need to explain these all here because the plaintiffs' experts relied basically on only one—strength of association. Id. at *8-*11. The district court walked through the basis for each expert's opinions, and one by one the court found heavy reliance on strength of association to the exclusion of other factors. Even then, one expert "was unwilling to identify what she perceived the strength of the association to be," and another "stopped short" of opining that the association was "strong" at all. Id. at *10-*11.

In the end, the district court found the experts' application of Bradford-Hill to be unreliable and "unduly result driven." In other words, "while plaintiffs' causation experts would be entitled to opine that there is an association between PDE5 use and melanoma progression, they have not reliability applied a Bradford-Hill analysis to make the requisite leap from correlation to causation." Id. at *11. The plaintiffs argued that the court could not exclude opinions just because it found them to be "shaky." But the court rejected that argument with this somewhat stinging rebuke:

Plaintiffs have been unable to point to any conclusion reached by any scientist, researcher, regulatory agency, or other qualified person or group apart from their experts in this litigation that use of PDE5 inhibitors causes melanoma progression. . . .

. . . [T]here simply is no interpretation by anyone other than plaintiffs' experts that supports general causation. On that critical question, despite substantial research on the issue over many years, plaintiffs' experts apparently stand alone. The unavoidable conclusion is that their weighing of the Bradford Hill factors does not represent a faithful application of an accepted methodology. The opinions must be excluded.

Id. at *12 (footnote omitted). Pretty strong stuff, but when you're right, you're right.

The plaintiffs did not come away empty handed: The district court denied the defendants' motion to exclude their experts on "biological plausibility." Id. at *6-*7. On that issue, laboratory studies purportedly allowed for a bona fide difference of scientific opinion, but we are not sure why that matters. Expert testimony on "biological plausibility" (which is one of the Bradford Hill causation criteria) is only helpful if there is a trial where someone is deciding causation, and without admissible general causation opinions, there shouldn't be a trial. We would go so far as to say there shouldn't be an MDL.

However this MDL proceeds, this order is a terrific lesson on the proper role of science in the courtroom. Regular readers of the blog know one of our favorite quotes: "Law lags science; it does not lead it." Rosen v. Ciba-Geigy Corp., 78 F.3d 316, 319 (7th Cir. 1996). The district judge in Viagra/Cialis clearly gets it, and because of that, we will give him the last word on how this is supposed to work:

Plaintiffs insist . . . that "science is heading towards causation." They have failed to show, however, how the evidence supports that characterization.

Instead, defendants' theme that "science has worked the way it is supposed to" is compelling. The Arozarena 2011 laboratory experiments suggested there could be an issue worth studying. Li 2014 took up the challenge in an epidemiological study. While it found an association, it cautioned that further research would have to be done before anyone should reach a conclusion . . . . In the ensuing years numerous other researchers have followed up, with studies that have been more robust in many ways. Those studies have consistently found an apparent association much smaller than that observed in Li 2014, and none of them has produced results that any person or organization other than plaintiffs' experts have believed support a conclusion of causation, or even of a degree of uncertainty that warrants additional precautions. . . .

Defendants' motion is granted . . . .

This article is presented for informational purposes only and is not intended to constitute legal advice.