In a recent opinion, Acosta v. Shell Western Exploration & Production, Inc., No. S-1-SC-33884, slip op. (N.M. Sup. Ct. March 3, 2016), the New Mexico Supreme Court reversed a decision by a state district court to exclude expert opinion testimony in a toxic tort case and, in doing so, announced further differences between federal and New Mexico law in determining the admissibility of scientific expert opinion testimony under the standards established by Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993) andState v. Alberico, 1993-NMSC-047, 116 N.M. 156, 861 P.2d 192.   While federal courts have continued to refine the standards for admissibility of expert testimony sinceDaubert, New Mexico courts have not necessarily followed these changes with respect to their application of Daubert/Alberico.  Compare Kumho Tire Co. v. Carmichael, 526 U.S. 137, 151 (1999) (extending the trial court's gate-keeping function under Daubert to include expert testimony based on nonscientific experience and training) with State v. Torres, 1999-NMSC-010, ¶ 43, 127 N.M. 20, 976 P.2d 20 (limiting the application of theDaubert/Alberico requirements to expert testimony that requires scientific knowledge).

In the underlying litigation, over two hundred residents of a residential development in Hobbs, New Mexico claimed that environmental contamination by the defendants' oil and gas operations on the site years earlier exposed them to toxic chemicals from crude oil and caused them to develop lupus and other autoimmune disorders. Acosta, No. S-1-SC-33884, ¶ 1.  In support of their claims, Plaintiffs sought to offer expert testimony of Dr. James Dahlgren that Plaintiffs' lupus and other autoimmune disorders were caused by long-term exposure to toxic chemicals found in crude oil.  Id. ¶ 6.  Dahlgren's causation opinion was supported by numerous animal and human studies wherein he found a correlation between the toxic chemicals Plaintiffs had been exposed to and autoimmune disorders, including lupus.  Id.  The district court excluded the studies as "not relevant, reasoning [that] they failed to show general causation between the mixture of identified chemicals and lupus."  Id. ¶ 17.  Specifically, the district court found that Dahlgren "had not considered the dose-response relationship necessary for inferring causation in humans from toxicological results in animals" and had "failed to bridge the gap from association to causation", such that the studies he relied on could not support Plaintiffs' claims that their exposure to toxic chemicals caused their lupus.  Id.  In support of its decision to exclude Dahlgren's causation testimony on grounds of relevance, the district court cited General Electric Co. v. Joiner, 522 U.S. 136, 146 (1997), for the proposition that "[a] court may conclude that there is simply too great an analytical gap between the data and the opinion proffered."  Acosta, No. No. S-1-SC-33884, ¶ 26. The New Mexico Court of Appeals also relied on Joiner in its opinion affirming the district court. See Acosta v. Shell W. Expl. & Prod., Inc., 2013-NMCA-009, ¶¶ 23-24, 27, 293 P.3d 917. 

Reversing the district court and the Court of Appeals, the New Mexico Supreme Court noted that "New Mexico has never adopted the Joiner rule that a judge may reject expert testimony where the ‘analytical gap' between the underlying evidence and the expert's conclusions is ‘too great,' see 522 U.S. [at] 146, and we refuse to do so in this case." Acosta, No. S-1-SC-33884, ¶ 27.  The Court explained that "[h]istorically, [it] has placed great value on allowing a jury to hear evidence and decide a case on the merits" and that "Joiner is inconsistent with longstanding New Mexico law that leaves credibility determinations and weighing of the evidence to the trier of fact."  Id. ¶¶ 27, 28.

Noting that a plaintiff must prove both general causation and specific causation in toxic tort cases and that "demonstrating that a chemical is capable of causing a particular injury in the general population is often difficult in first-exposure cases where it has not been the subject of extensive scientific analysis[,]" the Court expressed its agreement with other jurisdictions that such plaintiffs "should not be barred from having their day in court simply because scientific analysis on a particular chemical cause has not yet been fully developed."  Id. ¶¶ 30-31 (internal quotation marks and citations omitted).

Thus, the Court essentially held that it is acceptable for an expert to use his or her scientific judgment to bridge the gap between correlation and causation as long as the expert employs a reliable methodology in exercising his or her judgment and, in this case, Dahlgren's methodology was reliable.  See id. ¶¶ 32-33 ("In some cases where epidemiology is absent, jurists and scientists have employed the nonformulaic guidelines of Sir Austin Bradford Hill to assess whether an epidemiological study's finding of an association between a substance and an injury supported an inference of causation . . . In essence the Bradford Hill factors measure the ability of an epidemiological study to determine whether an association found by the study is sufficient to satisfy an ultimate question of fact regarding causation or whether the association is merely spurious . . . [A]pplication of the Bradford Hill factors in assessing general causation is widely accepted."). 

An expert's causation opinion, and the studies upon which that opinion is based, "are relevant and admissible if they demonstrate a valid scientific relationship that is probative of causation, regardless of their sufficiency to sustain [a plaintiff's] burden of proof."  Id.¶ 35.  In this case, the Court held that Dahlgren's studies showed that a harmful dose of toxic chemicals in mice, adjusted for the weight of humans, was comparable to the plaintiffs' dose, and the result of this extrapolation "is evidence that supports an inference of causation." Id. ¶ 39. "The credibility of the extrapolation and the weight it should be accorded," the Court said, "are questions for the jury."  Id.  

Having established an association between exposure to the toxic chemicals and the plaintiffs' diseases, the Court held that Dahlgren was able use his expert judgment to assess whether he had reliable support for an inference of causation.  See id. ¶ 40.  "Any questions regarding credibility of [Dahlgren's] judgment or interpretations is proper for the trier of fact to resolve."  Id.

In overturning the decision of the district court, the New Mexico Supreme Court held that the district court "improperly blurred the line between the district court's province to evaluate the reliability of Dahlgren's methodology and the jury's province to weigh the strength of Dahlgren's conclusions."  Id. ¶  41.  Ultimately, the Court concluded that Dahlgren's study and causation testimony should have been admitted because (1) he set forth the steps he took in arriving at his conclusions, (2) his reasoning, which included reliance on professional judgment, was based on scientific methodology of the kind traditionally used by experts addressing causation in toxicological epidemiology, and (3) the methodology of his study supported a valid scientific inference that was probative of causation, even if it did not conclusively establish that the specific chemicals at issue could cause lupus and other autoimmune disorders.