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Here is the third and final part of our 50-state opus on precedent supporting the principle that plaintiffs asserting claims dependent on propositions that ordinary people aren’t expected to know must come forward with expert opinions for those propositions.  As mentioned previously, this project arose from something we read about in the Mirena litigation – but it metastasized.  Part three covers from Pennsylvania through Wyoming.  Because we didn’t want to split Pennsylvania, this part is a little longer, and part two a little shorter, than average.

What we intend to do now, once our readers have had a chance to digest this, is consolidate the entire 50-state post in what is now part one of this survey.  That way, going forward, those of you who wish to consult this research will only have to look in one place.


Pennsylvania precedent is explicit that “[e]xpert testimony in support of the plaintiff’s claim is an indispensable requirement in establishing a plaintiff’s right of action” whenever “the treatment and injury typically involved are such that the common knowledge or experience of a layperson is insufficient to form the basis for passing judgment.”  Mitchell v. Shikora, 209 A.3d 307, 315 (Pa. 2019).  “[C]ausation is also a matter generally requiring expert testimony.”  Toogood v. Rogal, 824 A.2d 1140, 1145 (Pa. 2003).  Where “the complexities of the human body place questions as to the cause of pain or injury beyond the knowledge of the average layperson,” Pennsylvania requires expert testimony “that the injury in question did, with a reasonable degree of medical certainty, stem from” the act alleged.  Hamil v. Bashline, 392 A.2d 1280, 1285 (Pa. 1978).

Where, however, the ultimate determinations lie beyond the knowledge or expertise of the average layperson, expert testimony is permitted (and sometimes required) to aid the jury in its understanding of the factors involved and the teaching of the pertinent discipline with respect thereto. . . .   For a plaintiff to make out his cause of action in such a case, therefore, the law requires that expert medical testimony be employed.

Id. (citations omitted).  Accord, e.g., Smith v. German, 253 A.2d 107, 109 (Pa. 1969) (“plaintiff was required to offer expert testimony in order to establish the medical connection” to the accident); Dornon v. Johnston, 218 A.2d 808, 809 (Pa. 1966) (“expert guidance is necessary” whenever an issue is “sufficiently obscure that laymen are unable to make a reasonable determination as to its existence”); Grossman v. Barke, 868 A.2d 561, 567 (Pa. Super. 2005) (“causation is also a matter generally requiring expert testimony” because “a jury of laypersons generally lacks the knowledge to determine the factual issues”) (citation and quotation marks omitted); McMunn v. Babcock & Wilcox Power Generation Group., Inc., 869 F.3d 246, 267 (3d Cir. 2017) (“Expert evidence is generally required when an issue is beyond the ken of a lay jury.”) (applying Pennsylvania law); Cabrera v. Ross Stores, LP, 646 F. Appx. 209, 211 (3d Cir. 2016) (“expert testimony was necessary to establish the causation element of [plaintiff’s] suit”) (applying Pennsylvania law); Furlan v. Schindler Elevator Corp., 516 F. Appx. 201, 207 (3d Cir. 2013) (“[plaintiffs] were unable to meet their burden to establish a claim of negligent maintenance . . . with the exclusion of [their] expert testimony”) (applying Pennsylvania law); Gates v. Rohm & Haas Co., 655 F.3d 255, 265 (3d Cir. 2011) (“[e]xpert testimony is required to prove” the elements of medical monitoring) (quoting Sheridan v. NGK Metals Corp., 609 F.3d 239, 251 (3d Cir. 2010)) (applying Pennsylvania law); Estate of Aptekman v. City of Philadelphia, 127 F. Appx. 619, 622 (3d Cir. 2005) (“Where the causal nexus is not patently obvious, and there is no expert opinion, a factfinder could not simply infer a causal connection.”) (applying Pennsylvania law); In re TMI Litigation, 193 F.3d 613, 723 (3d Cir. 1999) (affirming summary judgment after affirming exclusion of plaintiffs’ experts) (applying Pennsylvania law); Redland Soccer Club, Inc. v. Dept. of Army, 55 F.3d 827, 852 (3d Cir. 1995) (quoting and following Hamil) (applying Pennsylvania law); N’Jai v. Bentz, 2016 WL 7404550, at *3 (W.D. Pa. Dec. 22, 2016) (“Pennsylvania and Federal courts have consistently rejected a plaintiff’s attempt to establish causation in a toxic tort case without supplying expert testimony.”), aff’d, 705 F. Appx. 126 (3d Cir. 2017); Ely v. Cabot Oil & Gas Corp., 2014 WL 12479991, at *10 (Mag. M.D. Pa. March 28, 2014) (“The law is well-established that claims for physical injury based upon alleged pollution or other torts generally require probative medical evidence.”), adopted, 2014 WL 12489767 (M.D. Pa. July 29, 2014); Kemmerer v. State Farm Insurance Co., 2004 WL 87017, at *3 (E.D. Pa. Jan. 19, 2004) (“In a case involving complex issues of causation not readily apparent to the fact finder, plaintiff must present admissible expert testimony to carry her burden.”); Fritz v Grossinger, 2009 WL 7039662 (Pa. C.P. Sept. 5, 2009) (“complex medical issues appertain to the determination of whether it was the remnant of the [medical device] . . . or some other cause that resulted in the alleged pain” and other injuries).

The same is true in Pennsylvania product liability litigation.  A “total lack of causation evidence absent the expert testimony . . . is a proper ground for summary judgment.”  Heller v. Shaw Industries, Inc., 167 F.3d 146, 165 (3d Cir. 1999) (applying Pennsylvania law).  “[E]xpert opinion on the effectiveness of the alternative design . . . [i]s required.”  Dunlap v. Federal Signal Corp., 194 A.3d 1067, 1073 (Pa. Super. 2018).

Pennsylvania law recognizes that proving the elements of these claims in complex tort cases often requires presentation of expert testimony. . . .  In other complex tort actions, such as product liability cases, courts have also opined that expert witnesses are often necessary to establish liability.  Further, courts recognize that there are consequences which flow from a failure to provide such proof.  Where a tort action turns on allegations of a technical nature relating to some alleged defect in a product, and the Plaintiff has failed to provide expert proof identifying the defect in the product or drawing a causal connection between that allegedly defective product and the Plaintiff’s injuries, courts have held that product liability and related negligence claims fail as a matter of law and must be dismissed.

Ruehl v. S.N.M. Enterprises, Inc., 2017 WL 5749560, at *1 (M.D. Pa. Nov. 28, 2017) (quoting American Power, LLC., v. Speedco Inc., 2017 WL 4084060, at *6 (M.D. Pa. Jan. 17, 2017) (citations omitted)).  See Nobles v. Staples, Inc., 150 A.3d 110, 120 (Pa. Super. 2016) (“exclusion of [plaintiff’s] expert made it impossible for [plaintiff] to prove” product liability even under a malfunction theory); Brandon v. Ryder Truck Rental, Inc., 34 A.3d 104, 110 (Pa. Super. 2011) (“an expert is necessary for [plaintiff] to prove his negligence claim against [defendant], and absent the testimony of a qualified expert, a jury’s verdict would be nothing more than conjecture”); Goldstein v. Phillip Morris, Inc., 854 A.2d 585, 589 (Pa. Super. 2004) (once plaintiff’s expert was “properly struck by the trial court . . . [plaintiff] had no means of establishing alleged specific defects in the [product]”); McCracken v. Ford Motor Co., 392 F. Appx. 1, 3 (3d Cir. 2010) (plaintiff “was required to support his claims of strict products liability and defective design with expert testimony”) (applying Pennsylvania law); Cabrera v. Ross Stores, LP, 646 F. Appx. 209 (3d Cir. 2016) (“expert testimony was necessary to establish the causation element of [plaintiff’s] suit”) (applying Pennsylvania law); Oddi v. Ford Motor Co., 234 F.3d 136, 159 (3d Cir. 2000) (“Inasmuch as [plaintiff’s] ‘defect expert’ does not survive Daubert scrutiny, the district court properly granted summary judgment to [defendants]”) (applying Pennsylvania law); Koplove v. Ford Motor Co., 795 F.2d 15, 18 (3d Cir. 1986) (“a rational jury could not find the defendant liable without some expert analysis of the available information which implicated it”) (applying Pennsylvania law); Bibbs v. SEPTA, 2012 WL 8704635, at *3 (Pa. Commw. April 13, 2012) (“Plaintiff was required to present expert testimony to establish that [product’s] defect . . . was the legal cause of Plaintiff’s injuries”); Hook v. Whiting Door Manufacturing Corp., 2019 WL 630324, at *6 (W.D. Pa. Feb. 14, 2019) (“where the issues in a products liability case are highly technical, expert testimony is necessary to assist the jury in understanding the claims”); White v. Home Depot, Inc., 2018 WL 2173960, at *4 (E.D. Pa. May 10, 2018) (summary judgment granted after defect expert excluded); McCracken v. R.J. Reynolds Tobacco Co., 2019 WL 635430, at *7 (E.D. Pa. Feb. 14, 2019) (quoting Lamar); Metil v. Core Distribution, Inc., 2018 WL 3707421, at *8 (W.D. Pa. Aug. 3, 2018) (“Absent [plaintiff’s] expert testimony relating to the cause of the accident and whether a design defect existed . . ., Plaintiff cannot support his theory of the case”); Bailey v. B.S. Quarries, Inc., 2017 WL 4366987, at *3 (M.D. Pa. Sept. 29, 2017) (“a product liability claim must be supported by expert witness testimony”); Hatcher v. SCM Group, Inc., 167 F. Supp.3d 719, 730 (E.D. Pa. 2016) (“without the expert report, there is no genuine dispute of material fact”); Inman v. General Electric Co., 2016 WL 5106939, at *9 (W.D. Pa. Sept. 20, 2016) (courts “routinely require plaintiffs to support their claims with expert testimony when the subject matter is highly technical and beyond the jury’s understanding”); Rabadi v. Great Wolf Lodge of the Poconos LLC, 2016 WL 4238638, at *5 (M.D. Pa. Aug. 9, 2016) (“Where, as here, a plaintiff fails to proffer the required expert evidence in response to a properly supported motion for summary judgment, summary judgment is appropriate.”) (citation and quotation marks omitted); Harris v. Oz Directional Drilling, Inc., 2016 WL 4578150, at *4 (Mag. M.D. Pa. June 30, 2016) (same as Ruehl), adopted, 2016 WL 4698635 (M.D. Pa. July 19, 2016); Webb v. Tahsin Industrial Corp., 2016 WL 454821, at *7 (M.D. Pa. Feb. 5, 2016) (“Lacking this expert evidence, Plaintiff’s claims must fail, and Defendant is entitled to an entry of summary judgment in its favor.”); Yoder v. Sportsman’s Guide, Inc., 2015 WL 7009547, at *12 (W.D. Pa. Nov. 12, 2015) (“the Court will enter summary judgment in Defendants’ favor as Plaintiffs do not present admissible expert evidence”); Rupert v. Ford Motor Co., 2015 WL 757402, at *9 (W.D. Pa. Feb. 23, 2015) (summary judgment granted after exclusion of plaintiff’s expert), aff’d, 640 F. Appx. 205 (3d Cir. 2016); Curry v. Royal Oak Enterprises, LLC, 2013 WL 3196390, at *7 (E.D. Pa. June 25, 2013) (“in a products liability case . . ., plaintiff must provide expert evidence to establish liability”) (citing Oddi); Ellis v. Beemiller, Inc., 910 F. Supp.2d 768, 774 (W.D. Pa. 2012) (“Expert testimony is required . . . if the subject matter is beyond the comprehension of the average juror”); Lamar v. Saks Fifth Ave., Inc., 2012 WL 12897909, at *2 (E.D. Pa. Oct. 23, 2012) (“under Pennsylvania law, in a case regarding the cause of pain or physical injury, a plaintiff must produce medical testimony”) (citing Hamil); Shecktor v. Louisville Ladder, Inc., 2012 WL 5052577, at *5 (M.D. Pa. Oct. 18, 2012) (“In the absence of that expert causation testimony . . . the Court is compelled to enter judgment in the Defendant’s favor.”); Westfield Insurance v. Detroit Diesel Corp., 2012 WL 1611311, at *4 (W.D. Pa. May 8, 2012) (“expert testimony is generally required in products liability cases where a defect is alleged, unless the issues are ‘simple’ and ‘within the range of comprehension of the average juror.’”); Mendoza v. Gribetz International, Inc., 2011 WL 2117610, at *3 (E.D. Pa. May 27, 2011) (“Expert testimony is generally required to sustain a products liability case.”) (citing Oddi); Maldonado v. Walmart Store No. 2141, 2011 WL 1790840, at *14 (E.D. Pa. May 10, 2011) (“Without the evidence of Plaintiff’s experts, Plaintiff has failed to offer sufficient evidence of causation”); Shannon v. Hobart, 2011 WL 442119, at *6 (E.D. Pa. Feb. 8, 2011) (“without expert testimony, a reasonable jury could not find from this evidence that the [product] contained a manufacturing or design defect that caused [plaintiff’s] injuries”); State Farm Fire & Casualty Co. v. Gopher Baroque Enterprises, Ltd., 2010 WL 5464767, at *6 (E.D. Pa. Dec. 29, 2010) (“Where the cause of an injury is arguably complex, a party must produce expert testimony on causation to survive a motion for summary judgment.”); Chubb v. On-Time Wildlife Feeders, 578 F. Supp.2d 737, 740 (M.D. Pa. 2008) (“Because a reasonable juror could not make a reasonable determination on [plaintiff’s] theory of liability without an expert witness, and [plaintiff’s] expert witness was precluded from testifying, there is no genuine issue of material fact to go to a jury.”); Thomas v. Hamilton Beach/Proctor-Silex, Inc., 2007 WL 2080485, at *7 (W.D. Pa. July 13, 2007) (“expert medical testimony is required to establish the requisite causal connection”); Marino v. Maytag Corp., 2005 WL 2403638, at *4 (W.D. Pa. Sept. 29, 2005) (“a juror could not look at the [plaintiff’s] evidence] without expert testimony to explain it”); Fabrizi v. Rexall Sundown, Inc., 2004 WL 1202984, at *12 (Mag. W.D. Pa. June 2, 2004) (“Where a plaintiff fails to present admissible expert testimony regarding causation, courts routinely have granted summary judgment in favor of the defendant.”) (citations omitted), adopted (W.D. Pa. June 24, 2004); Jones v. Toyota Motor Sales, USA, Inc., 282 F. Supp.2d 274, 277 (E.D. Pa. 2003) (“engineering, medical, and biomechanical analysis is not within the know-how of the ordinary layperson, and thus requires expert evidence”), aff’d, 94 F. Appx. 879 (3d Cir. 2004); Gower v. Savage Arms, Inc., 2002 WL 1833344, at *2 (E.D. Pa. June 12, 2002) (“Without expert testimony that the [product] was defective . . ., the plaintiffs cannot make out a design defect claim.”) (citations omitted); Booth v. Black & Decker, Inc., 166 F. Supp.2d 215, 223 (E.D. Pa. 2001) (“Without expert testimony, a reasonable jury could not find from this evidence that the [product] contained a manufacturing or design defect that defect caused the [accident].”); Rapp v. Singh, 152 F. Supp.2d 694, 707 (E.D. Pa. 2001) (“Absent such expert testimony, plaintiff cannot establish that the [product] was defective, or that [there is] a safer design.”); Chester Valley Coach Works, Inc. v. Fisher-Price, Inc., 2001 WL 1160012, at *13 (E.D. Pa. Aug. 29, 2001) (“Without his expert testimony, Plaintiffs lack sufficient evidence to establish the cause of the [accident].”); Pappas v. Sony Electronics, Inc., 136 F. Supp.2d 413, 427 (W.D. Pa. 2000) (“Absent [their expert’s] testimony, plaintiffs’ claims under Pennsylvania law cannot survive . . . summary judgment.”); Hodge v. Caterpillar, Inc., 1992 WL 98415, at *2 (E.D. Pa. April 30, 1992) (“expert opinion or analysis is a prerequisite to proof of a defective product”); Niklaus v. Vivadent, Inc., 767 F. Supp. 94, 96 (M.D. Pa. 1991) (“Pennsylvania law is clear that in a personal injury case when there is no obvious causal relationship between the accident and the injury, unequivocal medical testimony is necessary to establish the causal connection.”) (citation and quotation marks omitted); Blase v. Allied Signal, Inc., 36 Pa. D. & C.4th 491, 500 (Pa. C.P. 1996) (“complexities coupled with the intricacies of asbestos exposure require the presentation of expert medical testimony”).

The requirement for expert testimony is strongly enforced in Pennsylvania prescription medical product liability litigation.  In a medical device case, “the cause of [plaintiff’s] injury was something that could only be determined by the jury through expert medical testimony.”  Polett v. Public Communications, Inc., 126 A.3d 895, 931 (Pa. 2015).  “When the complexities of the human body place questions as to the cause of pain or injury beyond the knowledge of the average layperson, Pennsylvania requires expert testimony.”  Singer v. Eli Lilly & Co., 396 F. Appx. 715, 716 (2d Cir. 2010)) (applying Pennsylvania law).

In a case such as this one involving complex issues of causation not readily apparent to the finder of fact, plaintiff must present admissible expert testimony to carry her burden.  If [plaintiff’s] expert testimony cannot support both general and specific causation, summary judgment for the defendant must be granted.

Soldo v. Sandoz Pharmaceuticals Corp., 244 F. Supp.2d 434, 525 (W.D. Pa. 2003) (citing Heller).  Expert support is also mandatory in warning claims.

Expert testimony is admissible when it involves explanations and inferences not within the ordinary training, knowledge and experience of the jury. . . .  Certain questions cannot be determined intelligently merely from the deductions made and inferences drawn from practical experience and common sense.  On such issues, the testimony of one possessing special knowledge or skill is required in order to arrive at an intelligent conclusion.  In these matters, where laymen have no knowledge or training, the court and jury are dependent on the explanations and opinions of experts. . . .

Prescription drugs are likely to be complex medicines, esoteric in formula and varied in effect.  The terms and applications of a warning on such a drug, in order to have meaning, must be explained to the jury.  This is a subject so distinctively related to some science, profession, business or occupation as to be beyond the ken of the average layman.  Thus, we hold that in a complex products liability action such as this, expert testimony is required to determine whether the drug manufacturer’s warning to the medical community is adequate.

Dion v. Graduate Hospital, 520 A.2d 876, 881 (Pa. Super. 1987) (citations and quotation marks omitted).  See Demmler v. SmithKline Beecham Corp., 671 A.2d 1151, 1154 (Pa. Super. 1996) (“expert medical testimony is required to determine whether the drug manufacturer’s warning to the medical community is adequate”); Atkinson v. Ethicon, Inc., 2019 WL 3037304, at *4 (W.D. Pa. July 11, 2019) (“Plaintiffs’ claims fail because the claims require an expert report to establish causation”); In re Zoloft (Sertraline hydrochloride) Products Liability Litigation, 176 F. Supp.3d 483, 498 (E.D. Pa. 2016) (summary judgment granted; “Without admissible expert testimony . . ., Plaintiffs instead have cobbled together . . . biological plausibility, specific causation opinions based on an assumption that general causation has been established, and anecdotal evidence”) (footnote omitted), aff’d, 858 F.3d 787 (3d Cir. 2017); Young v. Pfizer, Inc., 2016 WL 1569472, at *3 (E.D. Pa. April 19, 2016) (Pennsylvania law “require[s] expert testimony when medical causation is at issue”); Kline v. Zimmer Holdings, Inc., 2015 WL 4077495, at *26 (W.D. Pa. July 6, 2015) (summary judgment granted; “the adequacy of a warning in prescription medical device cases generally must be proven by expert testimony”), aff’d, 662 F. Appx. 121 (3d Cir. 2016); Williams v. Wyeth, Inc., 2013 WL 3761107, at *2 (E.D. Pa. July 18, 2013) (“Plaintiff must provide expert medical testimony demonstrating that . . . Defendants’ products were a substantial factor in causing Plaintiff’s [injury]”); Fenelon v. Pfizer, Inc., 2012 WL 13173126, at *3 (S.D.N.Y. May 7, 2012) (“[w]ithout an expert, [plaintiff] cannot prove that [the drug] was the cause of [the] death”) (applying Pennsylvania law); Pusey v. Becton Dickinson & Co., 794 F. Supp.2d 551, 565 (E.D. Pa. 2011) (granting summary judgment after excluding plaintiff’s expert); Aaron v. Wyeth, 2010 WL 653984, at *9 (W.D. Pa. Feb. 19, 2010) (“the adequacy of a warning in prescription drug cases must be proven by expert testimony”); Mracek v. Bryn Mawr Hospital, 610 F. Supp.2d 401, 406 (E.D. Pa. 2009) (“without an expert report, [plaintiff] cannot establish that the [medical device] had a defect”), aff’d, 363 F. Appx. 925 (3d Cir. 2010); Dick v. American Home Products Corp., 2009 WL 1542773, at *4 (M.D. Pa. June 2, 2009) (“a plaintiff must produce expert medical testimony in order to prove that an allegedly defective product caused medical injury”); (lack of expert testimony was a “complete failure of proof as to this essential [causation] element of all of [plaintiff’s] claims [and] mandates the entry of summary judgment”); Perry v. Novartis Pharmaceuticals Corp., 564 F. Supp.2d 452, 473 (E.D. Pa. 2008) (“Because we have judged [plaintiff’s expert] evidence inadmissible . . ., we must also grant defendant’s motion for summary judgment.”); Soufflas v. Zimmer, Inc., 474 F. Supp.2d 737, 751 (E.D. Pa. 2007) (“Generally, the adequacy of a warning in prescription medical device cases must be proven by expert testimony.  This case is no different.”) (citing Demmler); Schmerling v. Danek Medical, Inc., 1999 WL 712591, at *10 (E.D. Pa. Sept. 10, 1999) (after experts excluded, “complete failure of proof as to [causation] of all of her claims mandates the entry of summary judgment”); O’Brien v. Sofamor, S.N.C., 1999 WL 239414, at *6 (E.D. Pa. March 30, 1999) (summary judgment granted after excluding plaintiff’s experts); Burton v. Danek Medical, Inc., 1999 WL 118020, at *5 (E.D. Pa. March 1, 1999) (“Absent admissible expert testimony that the [medical] device caused [their] injuries, Plaintiffs are unable to prevail on any of their claims.”); In re Risperdal Litigation, 2017 WL 3496520, at *5 (Pa. C.P. July 26, 2017) (“In the absence of expert testimony, Plaintiff cannot establish the warnings are inadequate.”) (citing Dion); Commonwealth v. Ortho-McNeil-Janssen Pharmaceuticals, Inc., 13 Pa. D. & C. 5th 187, 203 (Pa. C.P. 2010) (“expert medical testimony is required to determine whether the drug manufacturer’s warning to the medical community is adequate”); Lawrence v. Synthes, Inc., 2002 WL 32747667, at *24 (Pa. C.P. July 25, 2002) (“there can be no doubt that the medical cause of a complex condition such as is here presented requires expert evidence”), aff’d mem., 860 A.2d 1142 (Pa. Super. 2004).

Puerto Rico

The law in Puerto Rico holds that “a factfinder normally cannot find causation without the assistance of expert testimony to clarify complex medical and scientific issues that are more prevalent in medical malpractice cases than in standard negligence cases.”  Marcano Rivera v. Turabo Medical Center Partnership, 415 F.3d 162, 168 (1st Cir. 2005) (quoting Rojas-Ithier v. Sociedad Española de Auxilio Mutuo y Beneficiencia, 394 F.3d 40, 43 (1st Cir. 2005)) (applying Puerto Rico law).  “[T]he decisive consideration in determining the necessity of expert opinion evidence is whether the subject of inquiry is one of such common knowledge that persons of ordinary education could reach a conclusion as intelligently as the witness or whether, on the other hand, the matter is sufficiently beyond common experience that the opinion of an expert is required.”  Collazo-Santiago v. Toyota Motor Corp., 937 F. Supp. 134, 140 (D.P.R. 1996) (citation and quotation marks omitted), aff’d, 149 F.3d 23 (1st Cir. 1998).  See Velazquez v. Abbott Laboratories, 901 F. Supp.2d 279, 293 (D.P.R. 2012) (entering summary judgment on product liability claims because “plaintiffs have failed to introduce any expert testimony . . . to support their claims”).

The same rule applies to prescription medical products.  “[D]etermining when or if a given medication caused injuries when it was prescribed is the typical complex medical and scientific issue that . . . requires the assistance of a medical or scientific expert.”  Mercado-Velilla v. Asociacion Hospital del Maestro, 902 F. Supp.2d 217, 239 (D.P.R. 2012) (citation and quotation marks omitted).  See In re Bausch & Lomb Inc. Contacts Lens Solution Products Liability Litigation, 693 F. Supp.2d 515, 520 (D.S.C. 2010) (“this case involves complex medical causation questions . . . that are outside the realm of ‘common experience.’  Therefore, expert testimony is required under Puerto Rico law.”), aff’d, 429 F. Appx. 249 (4th Cir. 2011) (applying Puerto Rico law).

Rhode Island

Rhode Island precedent “is well settled that expert testimony is required to establish any matter that is not obvious to a lay person and thus lies beyond common knowledge.”  Rhode Island Resource. Recovery Corp. v. Restivo Monacelli LLP, 189 A.3d 539, 547 (R.I. 2018) (quoting Jessup & Conroy, P.C. v. Seguin, 46 A.3d 835, 839 (R.I. 2012)).  See Almonte v. Kurl, 46 A.3d 1, 18 (R.I. 2012) (same).  “[M]atters concerning [diseases] and [drug] therapy are not so obvious that the need for expert testimony is obviated.”  Young v. Park, 417 A.2d 889, 893 (R.I. 1980).

Thus, in product liability cases, the “we do not hesitate to conclude that the existence of a causal relationship between a particular toxin and its effect on the human body would have to be established through expert testimony.”  Mills v. State Sales, Inc., 824 A.2d 461, 468 (R.I. 2003).  Even as to products that “average lay persons use . . . every day, . . . only an expert who understands the[ir] mechanics . . . could understand and explain the [product] and whether a defect proximately caused an injury.”  Olshansky v. Rehrig International, 872 A.2d 282, 287 (R.I. 2005) (abrogated on other grounds, Cruz v. DaimlerChrysler Motors Corp., 66 A.3d 446 (R.I. 2013)).  See Hartford Insurance Co. v. General Electric Co., 526 F. Supp.2d 250, 260 (D.R.I. 2007) (“In the absence of such expert evidence . . ., Plaintiffs have not otherwise identified competent evidence upon which a reasonable jury could find that the alleged defect in the [product] was the proximate cause”).

South Carolina

“The general rule in South Carolina is that where a subject is beyond the common knowledge of the jury, expert testimony is required.”  Babb v. Lee County Landfill SC, LLC, 747 S.E.2d 468, 481 (S.C. 2013).  “[W]hen the medical question is a complicated one and likely to carry the fact-finding body into realms which are more properly within the province of medical experts,” “the subject is one for experts or skilled witnesses alone.”  Herndon v. Morgan Mills, Inc., 143 S.E.2d 376, 384 (1965).  “If [a plaintiff] is attempting to establish causation of a medically complex condition, however, expert medical testimony is required.”  Smith v. Michelin Tire Co., 465 S.E.2d 96, 97 (S.C. App. 1995).

Likewise, in South Carolina product liability cases, “expert evidence is required where a factual issue must be resolved with scientific, technical, or any other specialized knowledge.”  Watson v. Ford Motor Co., 699 S.E.2d 169, 175 (S.C. 2010).

Whether expert testimony is required is a question of law.  We have little trouble concluding as a matter of law that the [plaintiffs’] claim is one such case because it involves complex issues of computer science. . . .  [T]the design and structure of the software . . . is beyond the ordinary understanding and experience of laymen.  Hence, [plaintiffs] must support their allegations with expert testimony, and without it, their claims are subject to dismissal.

Graves v. CAS Medical Systems, Inc., 735 S.E.2d 650, 659 (S.C. 2012) (citations omitted).  See Oglesby v. General Motors Corp., 190 F.3d 244, 251 (4th Cir. 1999) (“Without [expert] testimony, [plaintiff] failed to meet his burden of proof.”) (applying South Carolina law); Green v. Bradley Co., 2017 WL 4012298, at *7 (D.S.C. Sept. 12, 2017) (“Absent the now-excluded testimony of [her expert], Plaintiff is unable to establish either the existence of a defect in the [product] at issue, or that a defect was the proximate cause of her injury − both essential elements of her claim.”), aff’d, 771 F. Appx. 184 (4th Cir. 2019); Morris v. Dorma Automatics Inc., 2013 WL 212587, at *6 (D.S.C. Jan. 18, 2013) (summary judgment granted where plaintiff “did not offer expert testimony”), aff’d, 537 F. Appx. 254 (4th Cir. 2013); Hickerson v. Yamaha Motor Corp., U.S.A., 2016 WL 4367141, at *4 (D.S.C. Aug. 16, 2016) (“without such expert testimony here to support Plaintiff’s claims of inadequate warnings, it would be difficult for this court to accept that a jury could find that the warnings . . . inadequate”), aff’d, 882 F.3d 476 (4th Cir. 2018); Stewart v. AT & T Mobility LLC, 2011 WL 3626654, at *5 (Mag. D.S.C. July 21, 2011) (“Without such admissible expert testimony to support a plaintiff’s theory of causation, the defendant is entitled to summary judgment.”), adopted, 2011 WL 3626641 (D.S.C. Aug. 17, 2011); Owens v. Hertz Equipment Rental Corp., 2010 WL 11534370, at *2 (D.S.C. Dec. 23, 2010) (“the use, operation, and maintenance of the [product] are technical matters which go beyond the scope of a lay person’s knowledge.  Therefore, Plaintiff must bring forth expert testimony to establish his burden of proof.”); Morehouse v. Louisville Ladder Group LLC, 2004 WL 2431796, at *9 (D.S.C. June 28, 2004) (“In the absence of [expert] testimony, Plaintiff is unable to establish that Defendant’s [product] was defective or that such defect caused Plaintiff’s accident.”).

Specifically, “[u]nder South Carolina law, in a [prescription medical product liability] case where a medical causation issue is not one within the common knowledge of the layman, the plaintiff must present medical expert testimony in order to establish causation.  Jones v. American Cyanamid Co., 139 F.3d 890, 1998 WL 116171, at *3 (4th Cir. 1998) (citation and quotation marks omitted) (applying South Carolina law).  “To establish defect and unreasonable danger in a medically complex [product liability] case, plaintiff must come forward with relevant and reliable expert testimony on these issues.”  King v. Stryker Corp., 2012 WL 12981763, at *4 (D.S.C. April 3, 2012) (citation and quotation marks omitted).  “Where a medical causal relation issue is not one within the common knowledge of the layman, proximate cause cannot be determined without expert medical testimony.”  In re Bausch & Lomb Inc. Contacts Lens Solution Products Liability Litigation, 693 F. Supp.2d 515, 518 (D.S.C. 2010), aff’d, 429 F. Appx. 249 (4th Cir. 2011).

[A] plaintiff [who] has not come forward with any proposed expert to offer biomechanical testimony . . . has no means of establishing how any proposed, theoretical modifications to the design of the [device] would function once implanted in the human body.  Without testimony necessary to fill this evidentiary gap, plaintiff cannot, as a matter of law, establish that the [device] was defective or unreasonably dangerous.

Disher v. Synthes (U.S.A.), 371 F. Supp.2d 764, 770 (D.S.C. 2005).  “Expert testimony is required where the claimant is ‘attempting to establish causation of a medically complex condition.’”  Jones v. Danek Medical, Inc., , 1999 WL 1133272, at *4 (D.S.C. Oct. 12, 1999) (emphasis original) (quoting Smith v. Michelin).  See Phelan v. Synthes (U.S.A.), 35 F. Appx. 102, 108-10 (4th Cir. 2002) (affirming summary judgment and exclusion of plaintiff’s expert); McClure v. Wyeth, 2012 WL 952856, at *1 (D.S.C. March 20, 2012) (“Under South Carolina law, expert testimony is necessary to establish causation for cases involving a complex medical condition”) (citing Smith); Jones v. Danek Medical, Inc., 1999 WL 1133272, at *4–5 (D.S.C. Oct. 12., 1999) (“granting summary judgment” when plaintiff failed to produce qualified expert to show causation in defective medical device case).

South Dakota

In South Dakota, “expert testimony is required when the issue falls outside the common experience of a jury.”  Burley v. Kytec Innovative Sports Equipment, Inc., 737 N.W.2d 397, 407 (S.D. 2007) (citing Caldwell v. John Morrell & Co., 489 N.W.2d 353 (S.D. 1992)).  “[A]bsent expert testimony, there is no basis for the jury to evaluate the actions of an ordinary prudent person.”  Id. at 408-09 (citation omitted).

Medical opinion on causation of physical injury is unnecessary only if the cause and effect are so immediate, direct and natural to common experience as to obviate any need for an expert medical opinion.  On the other hand, when symptoms are more separated in time from the accident, the causal relationship becomes more tenuous, necessitating expert testimony to prove causation.

Hanson v. Big Stone Therapies, Inc., 916 N.W.2d 151, 162 (S.D. 2018) (citations and quotation marks omitted).

Further, “in attempting to establish the elements of products liability, . . . [e]xpert testimony is generally necessary to establish elements of negligence and strict liability.”  Nationwide Mutual Insurance Co. v. Barton Solvents, Inc., 855 N.W.2d 145, 151 (S.D. 2014) (citation omitted).  “Plaintiff bore the burden to prove both liability and causation in a products liability action and expert testimony was necessary to provide ‘an evidentiary basis’ to successfully resist summary judgment.”  Cooper v. Brownell, 923 N.W.2d 821, 825 (S.D. 2019) (quoting Barton Solvents).  See Lindholm v. BMW of North America, LLC, 202 F. Supp.3d 1082, 1094 (D.S.D. 2016) (“it is not patently obvious that the accident would not have happened in the absence of a defect, and thus expert testimony is necessary to support Plaintiffs’ claims”), aff’d, 862 F.3d 648 (8th Cir. 2017); O’Neal v. Remington Arms Co., L.L.C., 2016 WL 1465351, at *3 (D.S.D. April 14, 2016) (Whether a plaintiff’s theory is based on strict liability or negligence, expert testimony is generally necessary to establish that a product is defective and that the defect proximately caused the plaintiff’s injury.”); Donat v. Trek Bicycle Corp., 2016 WL 297436, at *5 (D.S.D. Jan. 22, 2016) (“expert testimony is required when there is a complicated causation issue in a products liability case”); Jensen v. Hy-Vee, Corp., 2011 WL 1832997, at *4, 9 (D.S.D. May 13, 2011) (“expert testimony is required to help the jury determine whether . . . the alleged design defect caused [plaintiff’s] injuries” (citing Burley); “expert testimony establishing a causal connection between the lack of warning and [plaintiff’s] injuries is needed”).


Tennessee precedent requires that “[m]edical causation and permanency of an injury must be established in most cases by expert medical testimony.”  Thomas v. Aetna Life & Casualty Co., 812 S.W.2d 278, 283 (Tenn. 1991) (citations omitted).  “Typically, causation is established through expert medical testimony.”  Conner Brothers Excavating Co. v. Long, 98 S.W.3d 656, 660 (Tenn. 2003) (citing Thomas).

[W]hen the cause of an injury is not within the common knowledge of lay persons, expert medical evidence . . . is required.  Where an injury is complex or closely related to a pre-existing condition, expert evidence is critically important.  In these circumstances, the fact-finder cannot make a rational determination regarding whether the [defendant’s actions] caused the injury.

Austin v. Sneed, 2007 WL 3375335, at *11 (Tenn. App. Nov. 13, 2007) (citations omitted).  See Jones v. Firestone Tire & Rubber, 2001 WL 432528, at *3 (Tenn. April 27, 2001) (holding, in an asbestos exposure case, that “in all but the most obvious cases . . ., expert testimony is required to establish causation.  Proof of causation in this case must be shown by expert testimony.”) (citing Thomas).

In product liability cases, “[m]odern case law requires expert medical testimony to establish causation in cases where the plaintiff has suffered a complex injury.”  Smith v. General Motors Corp., 376 F. Supp.2d 664, 667 (W.D. Va. 2005), aff’d, 179 F. Appx. 890 (4th Cir. 2006) (for reasons stated by trial court) (applying Tennessee law).  To “establish[] the unreasonable dangerousness of a complex product about which an ordinary consumer has no reasonable expectation . . ., [t]he plaintiff must offer expert testimony.”  Brown v. Raymond Corp., 432 F.3d 640, 644 (6th Cir. 2005) (citation and quotation marks omitted).  With respect to a complex product, “without admissible expert testimony on causation and product defect, no reasonable jury could find for [plaintiff] because, under Tennessee law, expert testimony is required to establish liability in cases alleging manufacturing and design defects.”  Pride v. BIC Corp., 218 F.3d 566, 580 (6th Cir. 2000) (applying Tennessee law).  “Under Tennessee law, a plaintiff must provide admissible expert testimony as to both causation and product defect in order to prove liability in a products action. . . .  Moreover, under Tennessee law, medical causation must be established by expert testimony.”  Tomazin v. Lincare, Inc., 2015 WL 4545658, at *12 (M.D. Tenn. July 27, 2015) (citations omitted).  Thus, “[i]t is settled law that plaintiffs in a toxic tort case must present competent expert testimony . . . that links the individual plaintiff’s harm to the toxic substance allegedly causing the plaintiff’s injury.”  Spencer v. Synair Corp., 2005 WL 1719904, at *6 (E.D. Tenn. July 22, 2005) (quoting Nelson v. Tennessee Gas Pipeline Co., 2002 WL 1397253, at *2 (W.D. Tenn. June 11, 2002)).  See Whaley v. Rheem Manufacturing Co., 900 S.W.2d 296, 301 (Tenn. App. 1995) (plaintiff required expert testimony to demonstrate defect because the “workings of [the product] are beyond the common knowledge of laymen.”); Johnson v. Manitowoc Boom Trucks, Inc., 484 F.3d 426, 429 (6th Cir. 2007) (“expert testimony about the prudence of the decision to market becomes essential to [the] plaintiff’s case in chief” “because it involves establishing the unreasonable dangerousness of a complex product”) (citation and quotation marks omitted) (applying Tennessee law); Downs v. Perstorp Components, Inc., 26 F. Appx. 472, 477 (6th Cir. 2002) (“without admissible expert testimony on causation, no reasonable jury could find for plaintiffs because Tennessee law requires proof of causation for both strict liability and negligence actions”) (applying Tennessee law); Sanford v. L’Oreal USA S/D, Inc., 2017 WL 2376922, at *2 (M.D. Tenn. June 1, 2017) (where plaintiff “has failed to submit any testimony from a medical expert . . . there exists no material factual dispute regarding the cause of” her injuries); Coffey v. Dowley Manufacturing, Inc., 187 F. Supp.2d 958, 972 (M.D. Tenn. 2002) (“Plaintiffs will be unable to make out a claim for products liability without the use of an expert.  This product is simply too complex and too unfamiliar to ordinary consumers.”), aff’d, 89 F. Appx. 927 (6th Cir. 2003).

Prescription medical products are “complex products” under Tennessee law, requiring expert testimony.  In Jastrebski v. Smith & Nephew Richards, Inc., 1999 WL 144935 (Tenn. App. March 18, 1999), the court held:

Plaintiff’s testimony cannot substitute for the expert testimony required to establish a causal connection between an alleged defect in the product and a specific injury.  The product in dispute is a technically complex prescription medical device, and expert testimony is required to establish the causal connection between the alleged defect in the device and Plaintiff’s claimed injuries.

Id. at *6.  Jastrebski cited Fulton v. Pfizer Hospital Products Group, Inc., 872 S.W.2d 908, 912 (Tenn. App. 1993), which rejected use of res ipsa loquitur, holding that, where “the product in dispute is a technically complex medical device . . . expert testimony is required.”  Id. at 912.  See King v. Danek Medical, Inc., 37 S.W.3d 429, 449, 450, 461 (Tenn. App. 2000) (affirming summary judgment after concluding that plaintiff’s experts “failed to establish” either that “the defendants’ devices were unreasonably dangerous” or any “defective condition of the [medical device] implanted into the plaintiffs or causation”); Ward v. Cook, Inc., 2015 WL 3556060, at *2 (S.D.W. Va. June 4, 2015) (“medical causation must be established by testimony from a medical expert”) (applying Tennessee law); Shannon v. Apria Healthcare, Inc., 2011 WL 873458, at *5 (M.D. Tenn. March 4, 2011) (medical device case; “[w]ithout expert medical proof . . ., the factual allegations made by Plaintiff . . . cannot be sustained as a matter of law”); In re Aredia & Zometa Products Liability Litigation, 2009 WL 8638121, at *1 (M.D. Tenn. Aug. 13, 2009) (“Whether the warnings were adequate to warn a physician of the possibility that the drug might be causing the condition experienced must be presented through the testimony of an expert.”) (citations omitted);


“The general rule” in Texas “has long been that expert testimony is necessary to establish causation as to medical conditions outside the common knowledge and experience of jurors.”  Guevara v. Ferrer, 247 S.W.3d 662, 665 (Tex. 2007).  “[W]hen the causal link is beyond the jury’s common understanding, expert testimony is necessary.”  Alexander v. Turtur & Associates., Inc., 146 S.W.3d 113, 119-20 (Tex. 2004).  “The determination whether expert testimony is necessary is . . . a question of law.”  FFE Transportation Services, Inc. v. Fulgham, 154 S.W.3d 84, 89 (Tex. 2004).  Summing up:

Expert testimony is required when an issue involves matters beyond jurors’ common understanding.  Proof other than expert testimony will support a jury finding only when the jurors’ common understanding and experience will allow them to make that finding with reasonable probability.  . . .  The plaintiffs’ causation theory in this case is complex . . . [and] [w]e therefore hold that the plaintiffs must have supported their causation theory with expert testimony and objective proof.

Gharda USA, Inc. v. Control Solutions, Inc., 464 S.W.3d 338, 348 (Tex. 2015) (citations and quotation marks omitted).  See Bright v. Simpson, 2019 WL 1941885, at *4 (Tex. App. April 30, 2019) (“Without expert medical testimony, the evidence is legally insufficient to support a finding that the collision caused all of [plaintiff’s] damages.”); Zamora v. Champion Cooler Corp., 2018 WL 507362, at *2 (Tex. App. Jan. 23, 2018) (“expert testimony is necessary to establish causation regarding medical conditions outside the common knowledge and experience of jurors”); Cerny v. Marathon Oil Corp., 480 S.W.3d 612, 620 (Tex. App. 2015) (“The requirement of expert testimony is equally obvious in this case where [plaintiffs’] claims arise out of the alleged emissions and migration of hazardous substances”); Oncor Electric Delivery Co., LLC v. Southern Foods Group, LLC, 444 S.W.3d 699, 705 (Tex. App. 2014) (“Expert testimony is required when an issue involves matters beyond jurors’ common understanding.”) (citing Tamez); Dickerson v. State Farm Lloyd’s Inc., 2011 WL 3334964, at *14 (Tex. App. Aug. 3, 2011) (affirming both expert exclusions and summary judgment); Plunkett v. Connecticut General Life Insurance Co., 285 S.W.3d 106, 121 (Tex. App. 2009) (affirming summary judgment in toxic exposure case after affirming exclusion of plaintiffs’ experts); Brookshire Brothers, Inc. v. Smith, 176 S.W.3d 30, 36 (Tex. App. 2004) (“When a lay person’s general experience and common sense will not enable that person to determine causation, expert testimony is required.”); Feria v. Dynagraphics Co., 2004 WL 500869, at *9 (Tex. App. March 15, 2004) (“Because we find that the court did not abuse his discretion in excluding the expert witnesses tendered by [plaintiff], there was no evidence of causation presented to the court to defeat the defendants’ motions for summary judgment.”); Smith v. Southwest Bell Telephone Co., 101 S.W.3d 698, 702 (Tex. App. 2003) (“Proof that an injury to a specific body part extends to and affects the body generally must be supported by expert medical testimony and is not within the general experience of the jury.”).

Likewise, “[w]e have consistently required expert testimony and objective proof to support a jury finding that a product defect caused the plaintiff’s condition.”  Gharda, 464 S.W.3d at 348 (citations and quotation marks omitted).  In product liability cases, “[w]hether expert testimony is required depends on whether the issue involves matters beyond the general experience and common understanding of laypersons.”  Mack Trucks, Inc. v. Tamez, 206 S.W.3d 572, 583 (Tex. 2006).  “If juries were generally free to infer a product defect and injury causation from an accident or product failure alone, without any proof of the specific deviation from design that caused the accident, expert testimony would hardly seem essential.  Yet we have repeatedly said otherwise.”  Ford Motor Co. v. Ledesma, 242 S.W.3d 32, 42-43 (Tex. 2007) (citations omitted).  Texas law has “consistently required competent expert testimony and objective proof that a defect caused the [accident].”  Nissan Motor Co. Ltd. v. Armstrong, 145 S.W.3d 131, 137 (Tex. 2004).  Thus, “expert testimony is crucial in establishing that the alleged design defect caused the injury.”  Sims v. Kia Motors, Inc., 839 F.3d 393, 409 (5th Cir. 2016) (footnote omitted) (applying Texas law).

This case illustrates the type of complex causation theory that requires expert testimony and objective proof. . . .  Without such an expert, the plaintiffs have not met their burden of production under Texas law.  The plaintiffs’ failure to produce a fire expert who can identify the cause of the fire is therefore fatal to their success.

Smith v. Chrysler Group, L.L.C., 909 F.3d 744, 751-52 (5th Cir. 2018) (citations and footnotes omitted) (applying Texas law).  See BIC Pen Corp. v. Carter, 346 S.W.3d 533, 542 (Tex. 2011) (“Expert testimony is generally required in manufacturing defect cases to prove that the specific defect caused the accident.”); PHI, Inc. v. LeBlanc, 2016 WL 747930, at *8 (Tex. App. Feb. 25, 2016) (“whether [the product’s] design was defective involves a matter beyond the jurors’ common understanding, [so] we conclude that as a matter of law expert testimony was required”); Starr v. A.J. Struss & Co., 2015 WL 4139028, at *6 (Tex. App. July 9, 2015) (“Expert testimony is particularly necessary in toxic-tort and chemical-exposure cases, in which medically complex diseases and causal ambiguities compound the need for expert testimony.”) (citations omitted); iLight Technologies, Inc. v. Clutch City Sports & Entertainment, L.P., 414 S.W.3d 842, 851 (Tex. App. 2013) (“Expert testimony is generally required in manufacturing defect cases to prove that the specific defect caused the accident.”); Mata v. Energy Absorption Systems, LLC, 2011 WL 1233584, at *4 (Tex. App. March 31, 2011) (“competent expert testimony and objective proof that a defect caused the harm is required”); Lyon v. ATICO International USA, Inc., 2009 WL 1800820, at *2 (Tex. App. June 24, 2009) (“causation is not within a layperson’s general experience and common understanding; thus, expert testimony was required to establish a manufacturing defect”); Driskill v. Ford Motor Co., 269 S.W.3d 199, 205 (Tex. App. 2008) (“Because [plaintiffs] presented no expert testimony on causation . . ., there is less than a scintilla of evidence that the [product] was the cause-in-fact of the [incident] in this case.”); Poteet v. Kaiser, 2007 WL 4371359, at *3 (Tex. App. Dec. 13, 2007) (“a determination of causation in this case requires expert testimony”); Brown v. Rreef Management Co., 2007 WL 1829725, at *1 (Tex. App. June 27, 2007) (“Expert testimony is particularly necessary in chemical-exposure cases, in which medically complex diseases and causal ambiguities compound the need for expert testimony.”) (citation omitted); Hair v. Church & Dwight Co., 2004 WL 1615833, at *2 (Tex. App. July 20, 2004) (“Because [plaintiff] did not direct the trial court to any expert testimony that [defendant’s] product caused his injury, he did not raise a fact question on proximate cause.”); Sweeney v. Geon Co., 2002 WL 58223, at *4 (Tex. App. Jan. 17, 2002) (affirming summary judgment; “proving causation [here] requires expert testimony” because “causation of injuries from exposure to toxic chemicals is not readily ascertainable from general experience and common sense”); City of Dallas v. Furgason, 2007 WL 2703134, at *2 (Tex. App. Sept. 18, 2007) (“the record does not contain any expert testimony regarding either general or specific causation.  Thus, we conclude the evidence is legally insufficient to show the causal connection”); Norman v. Grove Cranes U.S., L.L.C., 750 F. Appx. 269, 273 (5th Cir. 2018) (“numerous intermediate Texas courts and federal district courts have granted judgments in favor of defendants where no admissible expert testimony was offered to prove the existence of a safer alternative design”) (citations omitted) (applying Texas law); Velasquez v. EAN Holdings, LLC, 2018 WL 5924037, at *9 (N.D. Tex. Nov. 13, 2018) (“Without expert testimony, Plaintiff has provided no evidence supporting his claim that the alleged condition of the [product], . . . proximately caused his injury.”); Carter v. Southstar Management, LLC, 2018 WL 5281791, at *5 (S.D. Tex. Oct. 24, 2018) (summary judgment granted “[b]ecause toxic tort cases require expert evidence of both general and specific causation, and there is no expert evidence on causation”); Deeds v. Whirlpool Corp., 2017 WL 3437772, at *13 (S.D. Tex. Aug. 10, 2017) (“Plaintiffs must have an expert witness for the defective product claims.”), aff’d, 764 F. Appx. 407 (5th Cir. 2019); Samuell v. Toyota Motor Corp., 2015 WL 1925902, at *5 (W.D. Tex. April 27, 2015) (“expert testimony is essential to both the existence of the defect and to its causation of injury”); Sedgwick v. BP Products North America, Inc., 2014 WL 6911543, at *3 (S.D. Tex. Nov. 4, 2014) (“Plaintiff’s claim is beyond the general experience of laypersons, and therefore requires expert testimony to establish both general and specific causation.”) (citation omitted); Romo v. Ford Motor Co., 798 F. Supp.2d 798, 809 (S.D. Tex. 2011) (“Courts applying Texas law in products liability actions have frequently required expert testimony for both defect and causation.”); In re Ford Motor Co. Speed Control Deactivation Switch Products Liability Litigation, 2011 WL 2518776, at *3 (E.D. Mich. March 29, 2011) (plaintiff’s expert’s “testimony is stricken, [and] Plaintiff does not have any evidence to support her burden of proving that a defective [product] caused the [incident]”) (applying Texas law); Kallassy v. Cirrus Design Corp., 2006 WL 1489248, at *4 (N.D. Tex. May 30, 2006) (“Without expert testimony, [plaintiff] cannot prove the existence of defect, an element essential to his strict product liability claims.”), aff’d, 265 F. Appx. 165 (5th Cir. 2008); Sigurdson v. Ford Motor Co., 2006 WL 417502, at *3 (S.D. Tex. Feb. 21, 2006) (“In light of the complete absence of expert testimony . . ., Defendant is entitled to summary judgment.”); Robinson v. Proctor & Gamble Distributing Co., 2004 WL 3019092, at *2 (N.D. Tex. Dec. 30, 2004) (“Because this Court struck Plaintiff’s expert on causation, she is left without any expert testimony”; “to the extent Plaintiff seeks damages for her [condition], she will be barred from recovery”).

In particular, “expert testimony is needed to satisfy the reasonable medical probability standard for establishing a causal link” in Texas prescription medical product cases.  Anderson v. Siemens Corp., 335 F.3d 466, 475 (5th Cir. 2003) (applying Texas law).  “Evidence of general causation in a drug case must be established through expert testimony.”  Wells v. SmithKline Beecham Corp., 2009 WL 564303, at *5 (W.D. Tex. Feb. 18, 2009), aff’d, 601 F.3d 375 (5th Cir. 2010).  “Texas courts have regarded expert testimony on causation as particularly vital in cases involving complex medical devices and medical diagnoses.”  Lewis v. Johnson & Johnson, 601 F. Appx. 205, 211 (4th Cir. 2015) (applying Texas law).

[E]xpert testimony is necessary to establish that Defendant’s alleged negligence in designing, assembling, inspecting, and maintaining the [medical device] (as well as failing to warn Plaintiff) proximately caused Plaintiff’s injuries.  Therefore, Plaintiff cannot escape his burden of offering expert testimony to support his causation theory merely by pleading that this is a case of simple negligence, rather than strict products liability.  In sum, Plaintiff’s failure to designate an expert to testify concerning proximate causation of his injuries is fatal to his case.

Morris v. National Seating & Mobility, Inc., 2019 WL 2343020, at *5 (Mag.W.D. Tex. June 3, 2019) (citations omitted).  See Burroughs Wellcome Co. v. Crye, 907 S.W.2d 497, 499-500 (Tex. 1995) (reversing verdict after excluding plaintiff’s expert); Johnson & Johnson v. Batiste, 2015 WL 6751063, at *4 (Tex. App. Nov. 5, 2015) (“proving the existence of a design defect requires competent expert testimony and objective proof that the defect the plaintiff has identified caused the injury”); Schronk v. Laerdal Medical Corp., 440 S.W.3d 250, 265 (Tex. App. 2013) (given “that the trial court did not err in excluding the testimony of [plaintiff’s experts], we cannot conclude that the trial court erred in granting summary judgment” to medical device manufacturer); Ethicon Endo-Surgery, Inc. v. Gillies, 343 S.W.3d 205, 212 (Tex. App. 2011) (since “the standard of care in marketing a specialized medical device requiring specialized technique for use is not within the experience of laymen, we must also conclude expert testimony was required to prove negligent marketing of such a device”); Minnesota Mining & Manufacturing Co. v. Atterbury, 978 S.W.2d 183, 203 (Tex. App. 1998) (“the plaintiffs’ experts failed to offer any reliable evidence of general causation” and “[i]n the absence of such evidence, the award of actual damages to the plaintiffs must therefore be reversed.”); Emerson v. Johnson & Johnson, 2019 WL 764660, at *3 (S.D. Tex. Jan. 22, 2019) (medical device “allegations involve complex and technical medical issues beyond jurors’ common understanding, knowledge, and experience, and therefore expert testimony on causation is required”); Tsao v. Ferring Pharmaceuticals, Inc., 2018 WL 3589097, at *7 (Mag. S.D. Tex. April 17, 2018) (“the nature, function, and potency of [a drug] . . . and its impact on [a] medically complicated process . . . are beyond the common knowledge and experience of laypersons”), adopted, 2018 WL 3589082 (S.D. Tex. June 13, 2018); Samuel v. Johnson & Johnson, 2015 WL 10793724, at *4 (E.D. Tex. Aug. 14, 2015) (expert testimony required to prove causation because “the nature and function of the prescription drug . . .  are outside the common understanding of a layperson.”); Christian v. Cook Inc., 2015 WL 3557242, at *2 (S.D.W. Va. June 4, 2015) (“the plaintiffs here must offer a medical expert . . . to testify on causation”) (citing Guevara) (applying Texas law); Gutierrez v. Arrow International, Inc., 2011 WL 13324082, at *9 (W.D. Tex. May 17, 2011) (“Absent expert testimony, [plaintiff] cannot raise a genuine issue of material fact that [the device] manufactured by the . . . defendants . . . caused or could cause him harm”); Wells v. SmithKline Beecham Corp., 2009 WL 564303, at *5 (W.D. Tex. Feb. 18, 2009) (“Evidence of general causation in a drug case must be established through expert testimony.”), aff’d, 601 F.3d 375 (5th Cir. 2010); Hohmann v. Shire Pharmaceuticals, 2008 WL 11388683, at *3 (S.D. Tex. July 3, 2008) (“Plaintiffs are required to produce expert testimony to satisfy the element of causation common to all of their claims”); In re Diet Drugs (Phentermine/Fenfluramine/Dexfenfluramine) Products Liability Litigation, 2008 WL 355517, at *2 (E.D. Pa. Feb. 8, 2008) (“Expert testimony regarding causation is therefore required”; without an expert, “Plaintiff has put forth no evidence that her alleged injury was caused by [defendant]s’ diet drugs”) (applying Texas law); Snee v. Zimmer, Inc., 2005 WL 8161446, at *2 (E.D. Tex. Sept. 16, 2005) (medical device case involves “complex issues of causation, undoubtedly requiring expert testimony and scientific analysis”); Kimble v. Danek Medical, Inc., 2000 WL 1468675, at *3 (S.D. Tex. Sept. 7, 2000) (“the effect of the implantation of a [medical] device . . . is not a matter of common knowledge or within the experience of a layperson” so “expert testimony is required on the issues of medical causation”) (citation and quotation marks omitted); Nobles v. Sofamor, S.N.C., 81 F. Supp.2d 735, 740 (S.D. Tex. 1999) (with plaintiff’s expert excluded, there is“no fact issue as to the presence of an instrument defect that caused [plaintiff’s] injury.”); Conger v. Danek Medical, Inc., 1998 WL 1041331, at *7 (N.D. Tex. Dec. 14, 1998) (exclusion of plaintiff’s experts means “Plaintiffs have not raised a genuine fact issue as to causation”); Leigh v. Danek Medical, Inc., 1998 WL 1041329, at *6 (N.D. Tex. Dec. 14, 1998) (with plaintiff’s experts excluded, “it is clear that plaintiff cannot raise a genuine issue of material fact as to causation”); Kelley v. American Heyer-Schulte Corp., 957 F. Supp. 873, 884 (W.D. Tex. 1997)  (“Due to . . . exclusion of expert testimony, the Plaintiff can present no evidence that [defendants’ devices] cause” the alleged injuries).


Utah law requires expert testimony on “scientific matters beyond the capacity of an ordinary juror.”  Graves v. North. Eastern. Services, Inc., 345 P.3d 619, 627 (Utah 2015).

[Where] the standard of care and the causal link between the negligence and the injury are usually not within the common knowledge of the lay juror, testimony from relevant experts is generally required in order to ensure that factfinders have adequate knowledge upon which to base their decisions.

Bowman v. Kalm, 179 P.3d 754, 755–56 (Utah 2008) (citation omitted).  “This is because the average lay juror is ill-equipped to sift through complicated medical evidence.”  Harris v. ShopKo Stores, Inc., 308 P.3d 449, 459 (Utah 2013).

In any type of case, “[i]n the absence of expert assistance, jurors would not likely possess the information or understanding necessary to make such assessments” involving “nuanced analysis of matters beyond the normal experience of the average layperson.”  Jenkins v. Jordan Valley Water Conservancy Dist., 321 P.3d 1049, 1053-54 (Utah 2013).  “[W]here the injury involves obscure medical factors which are beyond an ordinary lay person’s knowledge, necessitating speculation in making a finding, there must be expert testimony that the negligent act probably caused the injury.”  Fox v. Brigham Young University, 176 P.3d 446, 451–52 (Utah App. 2011) (citations and quotation marks omitted).  Moreover, “[i]t is only in the most obvious cases that a plaintiff may be excepted from the requirement of using expert testimony to prove causation.”  Id. (citation and quotation marks omitted).  See Hoopiiaina v. Intermountain Health Care, 740 P.2d 270, 271-72 (Utah App. 1987) (“In the absence of an expert to testify for plaintiff that the [drug] harmed him, . . . the jury would have no evidence upon which to base a finding that the [the drug] caused any harm to plaintiff.”); Pace v. Swerdlow, 519 F.3d 1067, 1073 (10th Cir. 2008) (“Because of the complex issues involved in a determination of proximate cause . . . Plaintiffs had to provide expert testimony.”) (citation and quotation marks omitted) (applying Utah law).

The same principles apply in Utah product liability and toxic tort cases.  “This court has held that medical expert testimony is required to prove proximate cause in a medical injury case.”  Fitz v. Synthes (USA), 990 P.2d 391, 393 (Utah 1999) (citation omitted).  In Fitz:

[Plaintiff] did not present any evidence supporting his medical causation claim, and the trial court would not allow his medical engineering expert to give an opinion on medical causation. . . .  In light of the foregoing, we conclude that . . . [plaintiff] failed to present evidence of medical causation.

Id. at 394.  In Reeves v. Geigy Pharmaceutical, Inc., “[t]he factual element underlying all [plaintiff’s] pleaded theories of liability is that his severe skin injuries were caused by [certain] drugs.”  764 P.2d 636, 640 (Utah App. 1988).  “Because these matters are outside the knowledge and experience of laypeople, expert medical testimony was required to establish causation, the standard of care, and its breach.”  Id.

Likewise, in warning cases, expert testimony is necessary because “[a] lay jury is not able to call on ‘their own life experiences’ to determine the adequacy of a drug label.”  Christison v. Biogen Idec, Inc., 199 F. Supp.3d 1315, 1340 (D. Utah 2016).  See King v. Searle Pharmaceuticals, Inc., 832 P.2d 858, 864 (Utah 1992) (“it cannot be concluded that an inference of [defendant’s] liability can be deduced from common experience and knowledge.  Accordingly, res ipsa loquitur is not sufficient to create a factual issue as to causation.”); Smith v. Terumo Cardiovascular Systems Corp., 2017 WL 2985749, at *4 (D. Utah July 12, 2017) (medical device case; “[m]edical causation (both but-for and proximate) must come from expert testimony (footnote omitted); Shipley v. Forest Laboratories, Inc., 2015 WL 4199739, at *4 (D. Utah July 13, 2015) (“In prescription drug cases, the causation element requires proof, usually in the form of expert testimony, of both general and specific causation.”) (citation omitted); Boucher v. Zimmer, Inc., 2010 WL 3815706, at *3 (D. Utah Sept. 27, 2010) (“because any testimony on the design of the [medical device] will present technically complex issues that are outside of the realm of jurors’ ordinary experience, Plaintiffs must offer admissible expert testimony in order to establish a design defect”); Coburn v. Smithkline Beecham Corp., 174 F. Supp.2d 1235, 1239 (D. Utah 2001) (“unclear . . . how Plaintiffs will establish that [a drug] was a cause of [plaintiff’s injuries] without eliciting expert testimony concerning general causation”).


Under Vermont law, “expert testimony is ordinarily required to prove medical causation.”  Sweet v. St. Pierre, 201 A.3d 978, 987-88 (Vt. 2018) (citation omitted).  “When the facts to be proved are such that any layman of average intelligence would know from his own knowledge and experience that the accident was the cause of the injury, no expert testimony is needed to establish the causal connection; however, where the causal connection is obscure, expert testimony is required.”  Egbert v. Book Press, 477 A.2d 968, 969 (Vt. 1984).  Where failure of an implanted medical device was at issue, “fault and causation are sufficiently complex as to be beyond the scope of common knowledge to a layperson”, so “that expert testimony was required to prove that theory.”  Taylor v. Fletcher Allen Health Care, 60 A.3d 646, 649-50 (Vt. 2012).  “While it is possible that the failure of the apparatus was a direct and proximate result of plaintiff’s fall, there is no way for a jury to intelligently evaluate the evidence without expert testimony.”  Id. at 651.

The same considerations apply to Vermont product liability and toxic tort litigation.  In Blanchard v. Goodyear Tire & Rubber, 30 A.3d at 1271 (Vt. 2011), a toxic tort case, summary judgment was appropriate where “[n]othing in [plaintiff’s expert’s] testimony was sufficient to support a jury finding of specific causation.”  Id. at 1278.  Thus, another Vermont court held:

[P]laintiffs in toxic exposure cases must demonstrate specific causation by submitting evidence concerning the amount, duration, intensity, and frequency of exposure.  In the absence of expert testimony, [plaintiffs] cannot establish these essential elements of their claims.

Dakers v. Bartow, 2018 WL 8415310, at *7 (D. Vt. Sept. 10, 2018) (Blanchard citation omitted).  In a drug case:

Plaintiffs must meet their burden of proving that ingestion of [the drug] caused the [injuries] in this case by offering expert testimony.  That expert testimony has been ruled inadmissible under Daubert.  Without expert testimony . . ., it is not possible to show that any inadequacy in warning about [the drug] was a substantial factor in bringing about the [those injuries].

Blanchard v. Eli Lilly & Co., 207 F. Supp.2d 308, 322 (D. Vt. 2002), see id. at 314 (“expert testimony is required to establish causation in this case”) (citations omitted).


“[E]xpert testimony is required” in Virginia to address any “complicated medical question that is not within the understanding of a lay person.”  Summers v. Syptak, 801 S.E.2d 422, 426 (Va. 2017).

Inasmuch as the causes of the injuries . . . are determinable only in the light of scientific knowledge, it has been recognized that expert testimony is usually necessary to support the conclusion as to causation.  The only exception to this requirement of expert testimony is the unusual case where the negligence and harmful results are sufficiently obvious as to lie within common knowledge.

Fitzgerald v. Manning, 679 F.2d 341, 350 (4th Cir. 1982) (citations and quotation marks omitted) (applying Virginia law).  See Williams v. Lowe’s Home Centers, Inc., 2018 WL 4699501, at *2 (Va. App. Oct. 2, 2018) (“when medical issues are complex, as in this case, causation must be determined by a medical expert”); Precision Pipeline, LLC v. Dominion Transmission, Inc., 2018 WL 3744018, at *3 (E.D. Va. Aug. 7, 2018) (“Without any expert testimony on the subject, [cross-plaintiff] cannot ask a lay jury to determine the complicated issue of causation.”); Clark v. Cobb, 2006 WL 6198463, at *4 (E.D. Va. Oct. 20, 2006) (“Plaintiff cannot establish the element of causation, an essential element of his negligence claim, without expert testimony”).

Virginia enforces the same requirements in toxic tort and product liability litigation.  “To prove causation in a toxic tort action, a plaintiff must offer relevant and reliable expert testimony, as the health effects of toxic exposure to chemicals are beyond the knowledge and experience of the average layperson.”  Zellers v. NexTech Northeast, LLC, 533 F. Appx. 192, 200 (4th Cir. 2013) (applying Virginia law).  Zellers affirmed the district court’s holding:

[I]n toxic tort cases, relevant and reliable expert testimony is required to prove (1) “that a particular chemical is harmful to humans generally,” i.e., general causation, and (2) “that exposure to the potentially harmful agent actually caused [the plaintiff’s injury],” i.e., specific causation.

Zellars v. NexTech Northeast, LLC, 895 F. Supp.2d 734, 739 (E.D. Va. 2012).

“Expert testimony is generally necessary to prove proximate causation in a products liability case.”  Schmitt-Doss v. American Regent, Inc., 2014 WL 3853184, at *8 (W.D. Va. Aug. 5, 2014), aff’d, 599 F. Appx. 71 (4th Cir. 2015) (for reasons stated by district court).  “[I]n a products liability action, proof of causation must ordinarily be supported by expert testimony because of the complexity of the causation facts.”  Kennedy v. Joy Technologies, Inc., 455 F. Supp.2d 522, 525 (W.D. Va. 2006), aff’d in pertinent part, 269 F. Appx. 302 (4th Cir. 2008) (applying Virginia law).  See Sanyal v. Toyota Motor North America, Inc., 2015 WL 3650725, at *7 (E.D. Va. June 11, 2015) (identical language); Cavallo v. Star Enterprise, 892 F. Supp. 756, 774 (E.D. Va. 1995) (“expert testimony is required to prove that exposure to a toxic substance caused a certain injury or illness”) (footnote omitted), aff’d in pertinent part, 100 F.3d 1150 (4th Cir. 1996).

For that proposition, both Kennedy and Sanyal quoted a prescription drug case, McCauley v. Purdue Pharma L.P., 331 F. Supp.2d 449, 464 (W.D. Va. 2004), demonstrating that expert testimony is required in prescription medical product liability litigation.  See Ball v. Takeda Pharmaceuticals America, Inc., 963 F. Supp.2d 497, 508, 510 (E.D. Va. 2013) (“plaintiff faces a fatal problem: she has no expert witness”; “[s]he must have expert testimony to meet her burden of proof”); Boysaw v. Purdue Pharma, 2008 WL 4452650, at *4 (W.D. Va. Sept. 30, 2008) (also quoting McCauley), aff’d, 320 F. Appx. 178 (4th Cir. 2009) (for reasons stated by district court); Evans v. Mentor Corp., 2005 WL 1667661, at *1 (E.D. Va. June 28, 2005) (also quoting McCauley); Hartwell v. Danek Medical, Inc., 47 F. Supp.2d 703, 707 (W.D. Va. 1999) (“[p]roof of legal causation in a medical device case must be by expert testimony”).

Virgin Islands

Virgin Islands law also follows “the general requirement of expert testimony on causation in a complex, toxic tort case.”  Henry v. St. Croix Alumina, LLC, 572 F. Appx. 114, 120 (3d Cir. 2014) (applying Virgin Islands law).  “[A] plaintiff is required to supply expert testimony in order to survive summary judgment on a design defect claim.”  Anders v. Puerto Rican Cars, Inc., 409 F. Appx. 539, 542-43 (3d Cir. 2011) (applying Virgin Islands law).  As the District Court explained in Anders:

[P]roving the existence of a defect in a product requires testimony from a qualified expert.  Where the issue concerns a product’s design, it would seem that expert opinion is the only available method to establish defectiveness, at least where the design is not patently defective.  Proving that an alleged defect was the legal cause of an injury requires testimony from a qualified expert who can testify about specific causation. . . .  Expert testimony offered by a competent expert who has an analytical and factual basis for his opinions should be required of plaintiffs in an automotive products liability case.

Anders v. Puerto Rican Cars, Inc., 2009 WL 3007367, at *9 (D.V.I. Sept. 15, 2009) (citations and quotation marks omitted), aff’d, 409 F. Appx. 539 (3d Cir. 2011).  See Washington v. HOVENSA, LLC, 2011 WL 6965855, at *1 (D.V.I. Dec. 13, 2011) (“[E]xpert testimony is required to prove causation in cases where the complexities of the human body place questions as to the cause of pain or injury beyond the knowledge of the average layperson.”) (internal quotations omitted).

Virgin Islands law follows the same principles in prescription medical product liability litigation:

Plaintiff’s case requires expert testimony to satisfy her burden with respect to both general causation and specific causation. In this case, “general causation” addresses the question of whether the ingredients of [drug] products are capable of causing [the relevant injury] in humans at therapeutic dose levels, while “specific causation” addresses whether those ingredients actually did cause [plaintiff’s injury].  If plaintiff’s expert opinion evidence regarding causation is inadmissible or insufficient to sustain a jury verdict in her favor, summary judgment is required to be granted to defendant.

Wade-Greaux v. Whitehall Laboratories, Inc., 874 F. Supp. 1441, 1475 (D.V.I. 1994) (citations omitted), aff’d mem, 46 F.3d 1120 (3d Cir. 1994).


Washington law holds that, when “[m]ust a patient present an expert medical opinion,” is a question “of law.”  Bauer v. White, 976 P.2d 664, 666 (Wash. App. 1999).

In general, expert testimony is required when an essential element in the case is best established by an opinion which is beyond the expertise of a layperson.  Expert testimony will generally be necessary to establish . . . most elements of causation. . . .  Medical facts must be proved by expert testimony unless they are observable by laypersons and describable without medical training.

Berger v. Sonneland, 26 P.3d 257, 267 (Wash. 2001) (footnotes omitted).  “Where the injury involves obscure medical factors which are beyond an ordinary lay person’s knowledge, necessitating speculation in making a finding, there must be expert testimony that the negligent act probably caused the injury.”  Riggins v. Bechtel Power Corp., 722 P.2d 819, 824 (Wash. App. 1986).  See Nikolayev v. Oyler, 143 Wash. App. 1012, 2008 WL 458649, at *2 (Wash. App. Feb. 21, 2008) (“The plaintiff must prove the causal relationship between the accident and his injuries.  And that requires expert testimony.”) (citation omitted); Cox v. Keg Restaurants U.S., Inc., 935 P.2d 1377, 1380 (Wash. App. 1997) (“Submitting the issue to the jury without such [expert] testimony is improper because the jury is thus invited to reach a result based on speculation and conjecture.”); Schudel v. General Electric Co., 35 F. Appx. 481, 484 (9th Cir. 2002). (“Because [plaintiff’s] injuries involved obscure medical factors and laypeople could not determine the injuries’ cause without resorting to speculation or conjecture, expert testimony was required to establish causation.”) (citation omitted) (applying Washington law); Bradley v. Wal-Mart Stores, Inc., 544 F. Supp.2d 1167, 1171 (W.D. Wash. 2008) (“A plaintiff must present medical testimony to establish the causal link between the injury and the incident.”).

The same is true in product liability.  “Expert testimony is required to establish causation when an injury involves obscure medical factors that would require an ordinary lay person to speculate or conjecture in making a finding.”  Bruns v. PACCAR, Inc., 890 P.2d 469, 477 (Wash. App. 1995).  See Koehler v. Allstate Insurance Co., 163 Wash. App. 1002, 2011 WL 3433304, at *7 (Wash. App. 2011) (“In the absence of any expert testimony supporting [plaintiff’s] allegations against [the product], the trial court properly granted summary judgment.”); McPhee v. Ford Motor Co., 135 Wash. App. 1017, 2006 WL 2988891, at *4 (Wash. App. Oct. 16, 2006) (summary judgment affirmed where plaintiff failed “to produce an affidavit from a qualified expert witness alleging specific facts that support a medical causation opinion”); Newkirk v. ConAgra Foods, Inc., 727 F. Supp.2d 1006, 1034 (E.D. Wash. 2010) (“in light of the exclusion of Plaintiffs’ [expert] evidence, Plaintiffs have failed to provide sufficient admissible evidence to support their burden of proof on any of their claims”), aff’d, 438 F. Appx. 607, 609 (9th Cir. 2011) (“Without the proffered expert testimony, [plaintiff] cannot show that [defendants] caused his disease.”); Henricksen v. ConocoPhillips Co., 605 F. Supp.2d 1142, 1177 (E.D. Wash. 2009) (“General causation and specific causation are essential elements of Plaintiffs’ prima facie case for each claim asserted in this litigation.  Expert testimony is necessary to make this showing since this is a toxic tort lawsuit.”) (citation omitted); Whisnant v. United States, 2006 WL 8442606, at *2 (W.D. Wash. Oct. 24, 2006) (“Fatal to plaintiffs’ case is the lack of expert testimony demonstrating the contaminants involved are capable of causing the specific ailments from which [she] suffers.”).

In cases involving use of prescription medical products, a plaintiff “ha[s] the burden of presenting expert medical testimony to demonstrate a causal link between the drug dose and the harmful effect.”  Smith v. Multicare Health System, 162 Wash. App. 1024, 2011 WL 2437797, at *2 (Wash. App. June 20, 2011).

[Plaintiff] must employ expert testimony if establishing this element would involve obscure medical facts requiring a lay person to speculate. . . .  [S]he must therefore present expert testimony assisting the jury in determining [the drug’s] impact on her and isolating it as a cause of her [injury]. . . .  Without this expert testimony, she cannot support a prima facie product liability action.

Sams v. Johnson & Johnson, 2015 WL 8213228, at *2 (W.D. Wash. Dec. 8, 2015) (citations omitted).

West Virginia

In West Virginia, “in a product liability case, the expert witness is ordinarily the critical witness.”  Morningstar v. Black & Decker Manufacturing Co., 253 S.E.2d 666, 682 (W.Va. 1979).  West Virginia law requires resort to expert testimony “where the injury is obscure, that is, the effects of which are not readily ascertainable, demonstrable or subject of common knowledge.”  Strahin v. Cleavenger, 603 S.E.2d 197, 211 (W. Va. 2004).

[W]here the exact nature and probable genesis of a particular type of injury involves complicated medical questions far removed from the ordinary experience and knowledge of laymen, only an expert can give competent opinion evidence as to the cause of the injury.

Turner v. Speedway LLC, 2015 WL 4392398, at *8 (S.D.W. Va. July 15, 2015) (citation and quotation marks omitted).

West Virginia “precedent reflects that expert testimony will be necessary to sustain an evidentiary burden when the matters involved are beyond the common knowledge and experience of the average juror.”  J.C. v. Pfizer, Inc., 814 S.E.2d 234, 243 (W. Va. 2018).  J.C., a prescription medical product liability case, held that expert testimony was critical to any evaluation of FDA-approved drug labeling.

[E]xpert testimony is necessary to sustain the burden of proof in complex cases involving matters of science, medicine, engineering, technology and the like. . . .  When the issues are beyond the common knowledge and experience of the average juror, expert testimony shall be required. . . .

[P]rescription drugs are likely to be complex medicines, esoteric in formula and varied in effect.  The terms and applications of a warning on such a drug, in order to have meaning, must be explained to the jury.  This is a subject so distinctively related to some science, profession, business or occupation as to be beyond the ken of the average layman.

*          *          *          *

The development of the [drug’s] label required the rendering of medical judgments as to whether essential information concerning risk is sufficiently conveyed; regulatory considerations; and how language in the label might be interpreted by physicians based upon how health services are provided in a given country.  Accordingly, . . . the subject matter . . . [is] not within the common knowledge and experience of the average juror and . . . [requires] expert testimony on the adequacy of the [drug’s] label.”  To find otherwise . . . would be to invite an unsound, unintelligent, and speculative verdict based upon matters beyond the cognition and experience of the average juror.

Id. at 246-47 (many citations and quotation marks omitted).

Thus, “when a claim involves highly complex matters of science, medicine, engineering, technology and the like, which are beyond the common knowledge and experience of the average juror, expert testimony will be necessary.”  Id. at 249.  See Watson v. Inco Alloys International, Inc., 545 S.E.2d 294, 303 (W. Va. 2001) (“questions involving the design of and appropriate warnings for [the product] are not within the common knowledge and experience of a lay juror” and require expert testimony); Addair v. Island Creek Coal Co., 2013 WL 1687833, at *3 (W. Va. April 17, 2013) (“complex illnesses that allegedly have arisen from exposure to chemicals of which the average person has no knowledge or experience” require expert testimony); Crawford v. General Motors Corp., 2007 WL 1960611, at *3 (N.D.W. Va. July 2, 2007) (“expert testimony is required in this case because the issue of whether [the product] was defectively designed or manufactured is well beyond the understanding of the average layman”).

Other West Virginia prescription medical product cases requiring expert testimony are:  Rohrbough v. Wyeth Laboratories, Inc., 916 F.2d 970, 972 (4th Cir. 1990) (“An essential element of plaintiffs’ cause of action is proof that defendant’s vaccine caused plaintiffs’ injuries, and proof of causation must be by expert testimony.”) (applying West Virginia law); Muzichuck v. Forest Laboratories, Inc., 2015 WL 235226, at *11 (N.D. W.Va. Jan. 16, 2015) (summary judgment granted where plaintiff “submitted no expert testimony supporting her proposed alternative means of warning”); Meade v. Parsley, 2010 WL 4909435, at *7 (S.D. W. Va. Nov. 24, 2010) (summary judgment granted enforcing “the general principle that causation evidence in toxic tort cases must be in the form of expert scientific testimony”).


Under Wisconsin law, “[e]xpert testimony is required to prove causation if the matter does not fall within the realm of ordinary experience and lay comprehension.”  Menick v. City of Menasha, 547 N.W.2d 778, 782 (Wis. 1996).  “Expert testimony is often required when unusually complex or esoteric issues are before the jury because it serves to assist the trier of fact.”  Pinter v. Village of Stetsonville, 929 N.W.2d 547, 558 (Wis. 2019) (citation and quotation marks omitted).  “The lack of expert testimony in cases which are so complex or technical that a jury would be speculating without the assistance of expert testimony constitutes an insufficiency of proof.”  Weiss v. United Fire & Casualty Co., 541 N.W.2d 753, 758 (Wis. 1995).

[T]he lack of expert testimony on the question of causation results in an insufficiency of proof where the issue involves technical, scientific or medical matters which are beyond the common knowledge or experience of jurors and the jury could only speculate as to what inference to draw.

Ollman v. Wisconsin Health Care Liability Insurance Plan, 505 N.W.2d 399 (Wis. App. 1993).

These principles apply in Wisconsin product liability and toxic tort litigation.  “[U]nder Wisconsin law, for Plaintiff to support his claims that chemical exposure caused him permanent injury, he must educe supporting qualified expert testimony.”  Kolesar v. United Agri Products, Inc., 412 F. Supp.2d 686, 696 (W.D. Mich. 2006) (applying Wisconsin law), aff’d, 246 F. Appx. 977, 981 (6th Cir. 2007).  A causation “conclusion without any support is not one based on expert knowledge and is not entitled to the dignity of evidence.  It has no scientific basis whatsoever.”  Smith v. Sofamor S.N.C., 21 F. Supp.2d 918, 921 (W.D. Wis. 1998).

Surgical . . . techniques and the adequacy of warnings from implant manufacturers are specialized medical issues and not within the realm of the ordinary experience of mankind”; expert testimony is required to support a defective-warning claim premised on this theory.

In re Zimmer, NexGen Knee Implant Products Liability Litigation, 884 F.3d 746, 753 (7th Cir. 2018) (citation omitted) (applying Wisconsin law).  See Jandrt v. Jerome Foods, Inc., 597 N.W.2d 744, 761 (Wis. 1999) (toxic tort plaintiff’s counsel properly sanctioned for “the absence of any scientific support for the underlying theory of causation . . . [o]nly an expert could have provided the critical link”); Johnson v. Mylan, Inc., 107 F. Supp.3d 967, 976 (E.D. Wis. 2015) (“The plaintiffs have no expert witness who can testify that [the device] was defective, or that it malfunctioned.  Pharmacology, toxicity, and . . . drug delivery are not matters within common knowledge or ordinary experience.”); Schultz v. Glidden Co., 2012 WL 968005, at *2 (E.D. Wis. March 21, 2012) (“To avoid summary judgment in a toxic tort case, the plaintiff must produce admissible expert testimony on the issue of both general and specific causation.”) (citation omitted), rev’d on other grounds, 721 F.3d 426 (7th Cir. 2013); Lemmermann v. Blue Cross Blue Shield, 713 F. Supp.2d 791, 813 (E.D. Wis. 2010) (“plaintiff has no evidence to support critical elements of her duty to warn or strict liability claims.  The expert testimony proffered by the plaintiff screams of unreliability”); Menges v. Depuy Motech, Inc., 61 F. Supp.2d 817, 824 (N.D. Ind. 1999) (“[p]roof of legal causation in a medical device case must be by expert testimony”) (applying Wisconsin law); Valente v. Sofamor, S.N.C., 48 F. Supp.2d 862, 877 (E.D. Wis. 1999) (summary judgment granted because “the plaintiffs fail to offer admissible expert testimony to show that the [medical] device designed, manufactured, promoted, distributed, and sold by the defendants caused the plaintiffs to sustain injuries”); Cali v. Danek Medical, Inc., 24 F. Supp.2d 941, 950 (W.D. Wis. 1998) (summary judgment granted after plaintiff’s experts excluded; “this is a case which requires medical testimony to establish causation between the device and plaintiff’s injury.”); Ruhland v. Walter Kidde Portable Equipment, Inc., 179 F.R.D. 246, 251 (W.D. Wis. 1998) (summary judgment granted; “this product liability action is sufficiently complex as to require expert testimony”).


Wyoming precedent requires expert testimony “[i]f the origin of the injury is obscure and not readily apparent to a layman, or if there are several equally probable causes of the condition.”  Sayer v. Williams, 962 P.2d 165, 168 (Wyo. 1998).  Thus, “expert testimony is required to establish causation unless the injury is immediately and directly or naturally and probably the result of an accident.”  Bodily v. State, 320 P.3d 240, 250 (Wyo. 2014).  See Harris v. Grizzle, 625 P.2d 747, 752 (Wyo. 1981) (“The rule . . . requiring expert testimony is applicable to the case at hand” involving use of a medical device).  In a product liability action, the Wyoming Supreme Court held:

[Plaintiff’s] case rested entirely on unsupported speculation by [an expert].  [Plaintiff] presented no admissible evidence which would indicate that the [product] was not reasonably safe when designed and manufactured; and, therefore, the court properly granted summary judgment

Campbell v. Studer, Inc., 970 P.2d 389, 394 (Wyo. 1998).

Similarly, Wyoming product liability actions involving prescription medical products require expert testimony.

[P]ersonal injury cases involving pharmaceuticals, toxins or medical devices involve complex questions of medical causation beyond the understanding of a layperson.  Complex causal relationships require expert testimony.  Accordingly, [plaintiff] must put forward expert testimony to survive summary judgment and dismissal of his case.

Ronwin v. Bayer Corp., 2008 WL 11427934, at *2 (D. Wyo. Oct. 1, 2008).  Plaintiff lacked admissible expert testimony, and summary judgment was entered.  Id. at *4 (“Without expert reports and testimony to establish a causal link between his seven month [drug] ingestion and his alleged physical injuries, [plaintiff] has failed to establish the existence of a genuine issue of material fact.”).  Summary judgment was affirmed on appeal.  Prescription medical product cases “involve[] complicated causation issues, [such that] all plaintiffs were required to present expert testimony to prove injury and a causal connection.”  Ronwin v. Bayer Corp., 332 F. Appx. 508, 514 (10th Cir. 2009) (“absent expert testimony on causation, summary judgment was appropriate”) (applying Wyoming law).