United States: Ninth Circuit Improperly Lowers Admissibility Bar For Expert Causation Testimony

Last Updated: November 23 2017
Article by David R. Geiger and Richard G. Baldwin

In Wendell v. GlaxoSmithKline LLC,1 the U.S. Court of Appeals for the Ninth Circuit reversed a trial court order2 that excluded expert testimony concerning the cause of a profoundly rare and deadly disease. The decision contravened multiple aspects of the U.S. Supreme Court's opinions on the admissibility of expert testimony and sets up a split among the federal circuits on the issue.


Plaintiffs' son Maxx died in 2007 at age 21 from hepatosplenic T-cell lymphoma (HSTCL), an "exceedingly rare and aggressive" form of non-Hodgkin's lymphoma. In 1999, following a diagnosis of inflammatory bowel disease (IBD), Maxx was prescribed six-mercaptopurine (6-MP), an immunosuppressant of the thiopurine class that was not specifically approved for IBD but was widely used for that purpose. In 2002, doctors added to his drug regimen infliximab, marketed as Remicade® and one of a class of anti-TNF drugs approved for treatment of autoimmune disorders such as Crohn's disease (a form of IBD).

When Maxx's IBD went into remission in 2006, he discontinued Remicade but remained on 6-MP. Two months later, the Food and Drug Administration approved a labeling change for Remicade that reported cases of HSTCL in young males with Crohn's disease treated with Remicade and a thiopurine. Accordingly, when Maxx's IBD symptoms returned he was prescribed a different anti-TNF drug whose label did not include this risk. He then stopped taking 6-MP in April 2007 after reading in a magazine article that young men taking both Remicade and an immunosuppressant had developed HSTCL. He also discontinued his anti-TNF drug in June. In July 2007, Maxx was diagnosed with HSTCL, and he succumbed to the disease five months later.

Following Maxx's death, his parents brought negligence and strict-liability claims under California law against six manufacturers and distributors of his various medications, alleging they had not adequately warned of the drugs' risks. Five years into the litigation, the remaining defendants moved for summary judgment arguing, among other things, that plaintiffs' causation experts' testimony was not scientifically reliable and was therefore inadmissible under Federal Rule of Evidence 702.

District Court Ruling

The U.S. District Court for the Northern District of California granted the motion, finding the opinions of plaintiffs' two causation experts—both medical doctors—not based on sufficiently reliable scientific data. The court first noted that a plaintiff claiming injury from a pharmaceutical must "establish that the substance at issue was capable of causing the injury alleged (general causation), and that the substance caused, or was a substantial factor in causing, the specific plaintiff's injury (specific causation)."

The court then recited the reliability standard and illustrative factors established by the Supreme Court in Daubert v. Merrell Dow Pharmaceuticals,3 including "whether the theory or technique in question can be (and has been) tested, whether it has been subjected to peer review and publication, its known or potential error rate and the existence and maintenance of standards controlling its operation, and whether it has attracted widespread acceptance within a relevant scientific community."

In Wendell, plaintiffs' experts (1) had never conducted any independent research or published any studies on the relationship between the drugs at issue and HSTCL, and indeed conceded their opinions would not satisfy the standard for peer-reviewed publication, and (2) failed to identify any animal or epidemiologic studies showing a causal link between HSTCL and the drugs. The absence of studies was of particular concern for HSTCL since more than 70 percent of cases were idiopathic, i.e., had no known cause.

As to the "handful" of studies and individual case reports plaintiffs' experts claimed to rely on (some of which were not even cited in their expert reports), they did not purport to show that the drugs caused HSTCL, only the incidence of that condition among different patient populations, including IBD patients. Nor did plaintiffs' experts opine that any increased incidence of HSTCL among IBD patients was statistically significant, or rule out alternative causes such as IBD itself either in the cited studies or in Maxx's individual case.

Problematic Ninth Circuit Ruling

On plaintiffs' appeal, the Ninth Circuit reversed. While calling it "a close question," the circuit court concluded the trial court had "looked too narrowly at each individual consideration, without taking into account the broader picture of the experts' overall methodology," and had "improperly ignored the experts' experience, reliance on a variety of literature and studies, and review of Maxx's medical records and history, as well as the fundamental importance of differential diagnosis by experienced doctors treating troubled patients." The Ninth Circuit also asserted the trial court had "overemphasized the facts that (1) the experts did not develop their opinions based on independent research and (2) the experts did not cite epidemiological studies."

The Ninth Circuit's opinion is problematic in multiple respects. First, although the court noted at the outset the abuse of discretion standard it was required to apply under the Supreme Court's decision in General Electric v. Joiner,4 in its actual analysis the court only referred back to this standard once. And its suggestion that the trial court had erred in viewing each missing indicium of reliability as somehow fatal by itself, rather than looking at total effect of all the experts' methodologic flaws, was simply not an accurate characterization of the trial court's ruling.

Second, the circuit court ultimately grounded its view that the district court had erred on the experts' qualifications and their purported use of a generally accepted "differential diagnosis" methodology in reaching their causation opinions. Regarding qualifications, the circuit court both began5 and ended6 its analysis with an emphasis on the experts' impeccable medical qualifications, including those specifically related to T-cell lymphoma. But Daubert and its progeny, and the current Federal Rule of Evidence 702, are unmistakably clear that the reliability of an expert's testimony is completely distinct from his qualifications. See F.R.E. 702 ("A witness who is qualified as an expert ... may testify in the form of an opinion or otherwise if ....").

As to a purported "differential diagnosis" methodology, the mere invocation of that term should not be a talisman sufficient to render reliable all expert testimony so labeled. Indeed, the use of the term here was actually a misnomer: the experts were not purporting to consider all the medically established conditions that might explain Maxx's symptoms so as to perform further testing and analysis to ultimately reach a diagnosis as to which of those diseases he suffered from. Rather, having already diagnosed him as suffering from HSTCL, they were purporting to opine as to the cause of that disease. Accordingly, they were actually applying a technique of differential causation or etiology.

Nor is this distinction merely semantic. As recognized by the district court, causation requires proof of both general and specific causation. Thus a proper differential-causation analysis requires the expert first to demonstrate what factors have been reliably established to cause the disease at issue in humans generally, and then to perform sufficient analysis reliably to exclude all but one of those factors for the individual in question (or at least to conclude that that factor among all those not excluded is more likely than not to be the specific cause).

In Wendell, the circuit court ignored general causation entirely and misunderstood the district court's concern about the lack of evidence showing a causal relationship in humans between HSTCL and the drugs at issue. Plaintiffs' experts could not rule out alternative causes such as IBD itself as explaining any increased incidence of HTSCL in the studies they cited. Regarding specific causation, neither the experts nor the circuit court explained how they could rule out idiopathic HSTCL in Maxx's case (in fact, the experts conceded they could not), or at least conclude the drugs were more likely the cause, when 70% of HSTCL cases are idiopathic.

At bottom, the Ninth Circuit's opinion appears driven by the concern that plaintiffs should not be disadvantaged by the fact that their son died from a disease that was quite rare, as a result of which the scientific community had developed very little relevant causation data.7 As the court stated, "The first several victims of a new toxic tort should not be barred from having their day in court simply because the medical literature, which will eventually show the connection between the victims' condition and the toxic substance, has not yet been completed."8

Of course, the court's suggestion that the medical literature "will eventually show the connection" assumes the very conclusion that was at issue in the case. In any event, the Ninth Circuit's view is squarely at odds with the approach taken by at least five other federal circuits, and indeed the Supreme Court. Among the circuits, the Seventh was the first to note that the requirement of a scientifically reliable basis for expert testimony necessarily means that "the courtroom is not the place for scientific guesswork, even of the inspired sort. Law lags science; it does not lead it."9 The Fifth,10 Sixth,11 Tenth12 and Eleventh13 Circuits have subsequently recognized this principle. And in Daubert itself, the Supreme Court noted: "We recognize that, in practice, a gatekeeping role for the judge, no matter how flexible, inevitably on occasion will prevent the jury from learning of authentic insights and innovations. That, nevertheless, is the balance that is struck by the Rules of Evidence."


In Wendell, the Ninth Circuit has recognized a new, lower bar for the admissibility of expert causation testimony in cases of new or rare diseases, under which judges may largely abdicate their gatekeeper role in deference to qualified experts who offer their professional judgment but lack true scientific support. The decision contradicts the commands of Daubert and Federal Rule of Evidence 702, invades the discretion afforded trial judges under Joiner, is contrary to the conclusion of five other circuit courts, and increases legal risk for the manufacturers of drugs and other substances that could conceivably have toxic effects.


1. 858 F.3d 1227 (9th Cir. 2017).

2. Wendell v. Johnson & Johnson, No. C 09-4124 CW, 2014 U.S. Dist. LEXIS 89576, 2014 WL 2943572 (N.D. Cal. June 30, 2014).

3. 509 U.S. 579, 593–94 (1993).

4. 522 U.S. 136 (1997).

5. 858 F.3d at 1233 ("To begin, the experts were highly qualified doctors.").

6. Id. at 1237 ("Where, as here, two doctors who stand at or near the top of their field and have extensive clinical experience with the rare disease or class of disease at issue, are prepared to give expert opinions supporting causation, we conclude that Daubert poses no bar based on their principles and methodology.").

7. The circuit court repeatedly referred to the rarity of HSTCL to excuse the experts' lack of support for their opinions. See id. at 1235 (expert opinion may be reliable without peer review and publication "especially ... when dealing with rare diseases); id. at 1236 (lack of animal or epidemiological studies "not surprising" because HSTCL is an "exceedingly rare cancer").

8. 8 858 F.3d at 1237 (quoting Clausen v. M/V New Carissa, 339 F.3d 1049, 1060 (9th Cir. 2003) (quoting Turner v. Iowa Fire Equip Co., 229 F.3d 1202, 1209 (8th Cir. 2000))) (internal quotations omitted).

9. Rosen v. Ciba-Geigy Corp., 78 F.3d 316, 319 (7th Cir. 1996).

10. Wells v. SmithKline Beecham Corp., 601 F.3d 375, 381 & n.33 (5th Cir. 2010) ("Perhaps [defendant's drug] is a cause of problem gambling, but the scientific knowledge is not yet there. [Plaintiff] urges the law to lead science—a sequence not countenanced by Daubert.").

11. Tamaraz v. Lincoln Elec. Co., 620 F.3d 665, 677 (6th Cir. 2010) ("Both sides agree that [plaintiff] is a good man who suffers from a terrible disease; we now force him to take the chance of prevailing at trial a second time, with less evidence than before. If he does not, yet it turns out ten years from now that [defendant's drug] causes his disease, that result will seem unfair. But the alternative route—allowing the law to get ahead of science—would be just as unfair.").

12. Hollander v. Sandoz Pharms. Corp., 289 F.3d 1193, 1217 (10th Cir. 2002).

13. Rider v. Sandoz Pharms. Corp., 295 F.3d 1194, 1202 (11th Cir. 2002) ("Given time, information, and resources, courts may only admit the state of science as it is. Courts are cautioned not to admit speculation, conjecture or inference that cannot be supported by sound scientific principles.").

Originally published in Washington Legal Foundation's Legal Backgrounder, November 2017.

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.

To print this article, all you need is to be registered on Mondaq.com.

Click to Login as an existing user or Register so you can print this article.

In association with
Related Topics
Related Articles
Related Video
Up-coming Events Search
Font Size:
Mondaq on Twitter
Register for Access and our Free Biweekly Alert for
This service is completely free. Access 250,000 archived articles from 100+ countries and get a personalised email twice a week covering developments (and yes, our lawyers like to think you’ve read our Disclaimer).
Email Address
Company Name
Confirm Password
Mondaq Topics -- Select your Interests
 Law Performance
 Law Practice
 Media & IT
 Real Estate
 Wealth Mgt
Asia Pacific
European Union
Latin America
Middle East
United States
Worldwide Updates
Registration (you must scroll down to set your data preferences)

Mondaq Ltd requires you to register and provide information that personally identifies you, including your content preferences, for three primary purposes (full details of Mondaq’s use of your personal data can be found in our Privacy and Cookies Notice):

  • To allow you to personalize the Mondaq websites you are visiting to show content ("Content") relevant to your interests.
  • To enable features such as password reminder, news alerts, email a colleague, and linking from Mondaq (and its affiliate sites) to your website.
  • To produce demographic feedback for our content providers ("Contributors") who contribute Content for free for your use.

Mondaq hopes that our registered users will support us in maintaining our free to view business model by consenting to our use of your personal data as described below.

Mondaq has a "free to view" business model. Our services are paid for by Contributors in exchange for Mondaq providing them with access to information about who accesses their content. Once personal data is transferred to our Contributors they become a data controller of this personal data. They use it to measure the response that their articles are receiving, as a form of market research. They may also use it to provide Mondaq users with information about their products and services.

Details of each Contributor to which your personal data will be transferred is clearly stated within the Content that you access. For full details of how this Contributor will use your personal data, you should review the Contributor’s own Privacy Notice.

Please indicate your preference below:

Yes, I am happy to support Mondaq in maintaining its free to view business model by agreeing to allow Mondaq to share my personal data with Contributors whose Content I access
No, I do not want Mondaq to share my personal data with Contributors

Also please let us know whether you are happy to receive communications promoting products and services offered by Mondaq:

Yes, I am happy to received promotional communications from Mondaq
No, please do not send me promotional communications from Mondaq
Terms & Conditions

Mondaq.com (the Website) is owned and managed by Mondaq Ltd (Mondaq). Mondaq grants you a non-exclusive, revocable licence to access the Website and associated services, such as the Mondaq News Alerts (Services), subject to and in consideration of your compliance with the following terms and conditions of use (Terms). Your use of the Website and/or Services constitutes your agreement to the Terms. Mondaq may terminate your use of the Website and Services if you are in breach of these Terms or if Mondaq decides to terminate the licence granted hereunder for any reason whatsoever.

Use of www.mondaq.com

To Use Mondaq.com you must be: eighteen (18) years old or over; legally capable of entering into binding contracts; and not in any way prohibited by the applicable law to enter into these Terms in the jurisdiction which you are currently located.

You may use the Website as an unregistered user, however, you are required to register as a user if you wish to read the full text of the Content or to receive the Services.

You may not modify, publish, transmit, transfer or sell, reproduce, create derivative works from, distribute, perform, link, display, or in any way exploit any of the Content, in whole or in part, except as expressly permitted in these Terms or with the prior written consent of Mondaq. You may not use electronic or other means to extract details or information from the Content. Nor shall you extract information about users or Contributors in order to offer them any services or products.

In your use of the Website and/or Services you shall: comply with all applicable laws, regulations, directives and legislations which apply to your Use of the Website and/or Services in whatever country you are physically located including without limitation any and all consumer law, export control laws and regulations; provide to us true, correct and accurate information and promptly inform us in the event that any information that you have provided to us changes or becomes inaccurate; notify Mondaq immediately of any circumstances where you have reason to believe that any Intellectual Property Rights or any other rights of any third party may have been infringed; co-operate with reasonable security or other checks or requests for information made by Mondaq from time to time; and at all times be fully liable for the breach of any of these Terms by a third party using your login details to access the Website and/or Services

however, you shall not: do anything likely to impair, interfere with or damage or cause harm or distress to any persons, or the network; do anything that will infringe any Intellectual Property Rights or other rights of Mondaq or any third party; or use the Website, Services and/or Content otherwise than in accordance with these Terms; use any trade marks or service marks of Mondaq or the Contributors, or do anything which may be seen to take unfair advantage of the reputation and goodwill of Mondaq or the Contributors, or the Website, Services and/or Content.

Mondaq reserves the right, in its sole discretion, to take any action that it deems necessary and appropriate in the event it considers that there is a breach or threatened breach of the Terms.

Mondaq’s Rights and Obligations

Unless otherwise expressly set out to the contrary, nothing in these Terms shall serve to transfer from Mondaq to you, any Intellectual Property Rights owned by and/or licensed to Mondaq and all rights, title and interest in and to such Intellectual Property Rights will remain exclusively with Mondaq and/or its licensors.

Mondaq shall use its reasonable endeavours to make the Website and Services available to you at all times, but we cannot guarantee an uninterrupted and fault free service.

Mondaq reserves the right to make changes to the services and/or the Website or part thereof, from time to time, and we may add, remove, modify and/or vary any elements of features and functionalities of the Website or the services.

Mondaq also reserves the right from time to time to monitor your Use of the Website and/or services.


The Content is general information only. It is not intended to constitute legal advice or seek to be the complete and comprehensive statement of the law, nor is it intended to address your specific requirements or provide advice on which reliance should be placed. Mondaq and/or its Contributors and other suppliers make no representations about the suitability of the information contained in the Content for any purpose. All Content provided "as is" without warranty of any kind. Mondaq and/or its Contributors and other suppliers hereby exclude and disclaim all representations, warranties or guarantees with regard to the Content, including all implied warranties and conditions of merchantability, fitness for a particular purpose, title and non-infringement. To the maximum extent permitted by law, Mondaq expressly excludes all representations, warranties, obligations, and liabilities arising out of or in connection with all Content. In no event shall Mondaq and/or its respective suppliers be liable for any special, indirect or consequential damages or any damages whatsoever resulting from loss of use, data or profits, whether in an action of contract, negligence or other tortious action, arising out of or in connection with the use of the Content or performance of Mondaq’s Services.


Mondaq may alter or amend these Terms by amending them on the Website. By continuing to Use the Services and/or the Website after such amendment, you will be deemed to have accepted any amendment to these Terms.

These Terms shall be governed by and construed in accordance with the laws of England and Wales and you irrevocably submit to the exclusive jurisdiction of the courts of England and Wales to settle any dispute which may arise out of or in connection with these Terms. If you live outside the United Kingdom, English law shall apply only to the extent that English law shall not deprive you of any legal protection accorded in accordance with the law of the place where you are habitually resident ("Local Law"). In the event English law deprives you of any legal protection which is accorded to you under Local Law, then these terms shall be governed by Local Law and any dispute or claim arising out of or in connection with these Terms shall be subject to the non-exclusive jurisdiction of the courts where you are habitually resident.

You may print and keep a copy of these Terms, which form the entire agreement between you and Mondaq and supersede any other communications or advertising in respect of the Service and/or the Website.

No delay in exercising or non-exercise by you and/or Mondaq of any of its rights under or in connection with these Terms shall operate as a waiver or release of each of your or Mondaq’s right. Rather, any such waiver or release must be specifically granted in writing signed by the party granting it.

If any part of these Terms is held unenforceable, that part shall be enforced to the maximum extent permissible so as to give effect to the intent of the parties, and the Terms shall continue in full force and effect.

Mondaq shall not incur any liability to you on account of any loss or damage resulting from any delay or failure to perform all or any part of these Terms if such delay or failure is caused, in whole or in part, by events, occurrences, or causes beyond the control of Mondaq. Such events, occurrences or causes will include, without limitation, acts of God, strikes, lockouts, server and network failure, riots, acts of war, earthquakes, fire and explosions.

By clicking Register you state you have read and agree to our Terms and Conditions