Michael J. Hutter
Michael J. Hutter ()

The 2013-14 term of the Court of Appeals has produced—so far—three significant decisions from the court discussing the admissibility of expert testimony and the trial court’s “gatekeeping” role—Matter of State v. Floyd Y., 22 N.Y.3d 95 (2013); People v. Oddone, 22 N.Y.3d 364 (2013); and Cornell v. 360 West 51st Street Realty, 2014 N.Y. Slip Op. 02096 (March 27, 2014). Floyd Y. and Oddone were discussed at length in two prior columns. (See, Hutter, “‘Floyd Y.’: The Professional Reliability Basis for Expert Opinion,” NYLJ, Dec. 5, 2013, p. 3, col. 1; Hutter, “‘Oddone’: Frye’s (Non)-Applicability to Experience-Based Expert Opinion,” NYLJ, Feb. 6, 2014, p. 3, col. 1). This column will discuss Cornell.1

In Cornell, the court held that the expert opinion in issue was not admissible because Frye’s “general acceptance” standard was not met by “some support” in the scientific literature, and the expert’s “differential diagnosis” was insufficient to establish a foundation for the opinion in any event. Differential diagnosis is a generally accepted methodology by which a physician considers the known possible causes of a patient’s symptoms and then by utilizing diagnostic tests eliminates causes from the list until the most likely cause remains.

While Cornell involved a claim that exposure to toxic mold caused a variety of personal injuries, its elucidation of the “general acceptance” standard as set forth in Frye v. United States, 293 F. 1013 (D.C. Cir. 1923), and the foundation standard as set forth in Parker v. Mobil Oil, 7 N.Y.3d 434, 447 (2006), is not limited to toxic tort cases. Rather, Cornell will have an impact in all tort cases where expert testimony is proffered to explain to the jury the mechanism of a plaintiff’s injury.


Analysis starts with an understanding of the facts and the competing expert opinions offered by plaintiff and defendants. Plaintiff Brenda Cornell alleged that she sustained a variety of personal injuries caused by exposure to toxic mold in her apartment. Her apartment was located directly above the basement, which sustained water damage from flooding in 2002 and 2003. In July 2003, after a steam pipe broke in her apartment, plaintiff noticed a small amount of mold and she developed a rash, shortness of breath, fatigue, disorientation and headaches. The symptoms disappeared after the owner, defendant 360 W. 51st Street Corp., installed a dehumidifier and she washed the area with bleach.

In September 2003, 360 W. 51st Street Corp. sold the apartment building to defendant 360 West 51st Street Realty. The new owner began renovating the basement a month later. As soon as debris removal began, plaintiff developed the same symptoms she had in July, as well as congestion, swollen eyes and a metallic taste in her mouth. Despite taking prescribed allergy medication, the symptoms only subsided when she left her apartment for a period of time.

Defendants moved for summary judgment seeking dismissal of plaintiff’s alleged toxic mold-caused injuries. The motion was premised on plaintiff’s inability to satisfy the applicable Frye standard, namely, the absence of proof of general acceptance in the relevant scientific community of her theory that exposure to indoor mold can cause her complained of condition, and the absence of a sufficient foundation supporting the conclusion that plaintiff’s illness was caused by her claimed exposure, as required by Parker.

Defendants’ expert, a clinical immunologist, opined that there was “no relationship between the medical problems experienced by [plaintiff] and exposure to mold.” Cornell, 2014 NY Slip Op. 02096 at *4. This opinion was principally based upon a paper of the American Academy of Allergy, Asthma and Immunology, a paper the expert stated reflected the generally accepted “state of the art” and was authoritative, concluding that while exposure to molds can cause human disease through several well-defined mechanisms, exposure to indoor mold has not been demonstrated to have that casual connection. Id. at *5-6.

The expert further opined that even if there were some sufficient causal connection between human disease and exposure to indoor molds, plaintiff could not show that her claimed injuries were the result of her claimed exposure as, among other things, her claimed injuries “are common in the human population regardless of indoor exposure to molds” and molds “have never been shown to cause other physical and psychological problems that Cornell ascribes to indoor mold exposure (e.g., cognitive problems, seizures, depression).” Id. at *6.

Plaintiff opposed the motions with an affidavit from her expert, a doctor of environmental and occupational medicine, who specialized in mold-related illness. He opined that plaintiff’s complained of medical problems were “undeniably caused by exposure to an unusual mixture of atypical microbial contaminants.” Id. at *7. The basis for this opinion was several studies stating that various mold byproducts “may have adverse effects to humans,” government reports, guidelines and public health instructions that stated indoor mold exposure is a public health risk and concern, and that there is sufficient evidence of “associations” of building dampness with the presence of mold, Id. at *7-8, which was sufficient to satisfy Frye. The expert’s further conclusion that plaintiff’s complained of health problems were in fact caused by her exposure to mold in her apartment building was made through a differential diagnosis method, which satisfied Parker. Id. at *9.

Supreme Court (Marcy S. Freidman, J.) granted the motions for summary judgment, concluding that plaintiff’s expert opinion was insufficient to raise a triable issue of fact on her mold-causation claim. 2009 NY Slip Op. 52707(U).2 The First Department, with Justice James Catterson dissenting, reversed the Supreme Court’s dismissal, finding that plaintiff’s expert’s opinion was sufficient to raise a triable issue of fact. 95 A.D.3d (2012). The majority was of the view that the opinion was sufficient because it had “some support” in existing data, studies and literature, thereby satisfying Frye, and the expert had reached his conclusions as to causation on the basis of his performance of a differential diagnosis, thereby satisfying Parker. Catterson expressed his disagreement with the majority’s Frye conclusion that the expert’s theory was shown to be generally accepted within the relevant scientific community. Id. at 63.

The Court of Appeals, in a comprehensive and thoughtful opinion written by Judge Susan Read, reversed and granted summary judgment dismissing the complaint. The basis for this reversal was the court’s conclusion that plaintiff’s expert’s opinion was insufficient under the Frye standard because an “association” and “some support” in the relevant literature are insufficient to support Frye’s requirement that the relevant scientific community generally accepts that “molds cause those [claimed] adverse health effects;” and the performance of a differential diagnosis was insufficient to support his opinion under Parker. Cornell, 2014 NY Slip Op. 02096 at *17-20 (emphasis by court).

Chief Judge Jonathan Lippman and Judge Eugene Pigott dissented in an opinion written by Pigott. Their dissent was premised on the fact that there is no dispute among experts that there are causal links between exposure to mold and respiratory illnesses. With this undisputed fact, whether that “association” is indicative of a causal relationship in this case was necessarily a question of fact for the jury. Id. at *20-21.

‘Cornell’ Takeaways

Initially, the unmistakeable thrust of the court’s opinion is to assure the evidentiary reliability of expert testimony before it is heard by the jury. This is accomplished by the imposition of a “gatekeeping” function upon the trial court under which it is charged with the task of ensuring that an expert’s opinion rests upon a reliable foundation. This reliability task has two components, both focusing upon the methodology used by the expert in reaching his opinion from the facts relied upon.3

Under the Frye component, where the expert’s methodology involved novel scientific principles or procedures, the trial court must determine whether that principle or procedure is “sufficiently established to have gained general acceptance in the particular field in which it belongs.”4 Under the Parker component the inquiry is whether the principle or methodology, regardless of whether it is novel, was “appropriately employed.”5 As noted in Parker, in a foundation inquiry, “[t]he focus moves from the general reliability concerns of Frye to the specific reliability of the procedures followed to generate the evidence proffered and whether they establish a foundation for the reception of the evidence at trial.”6

While some Appellate Division decisions have cautioned against applying these inquiries too restrictively, including the First Department below, the court rejected such an approach and instead stressed that the trial court’s gatekeeper function requires a rigorous examination of the methodology and how the expert applied it to the case at hand. Cornell, 2014 NY Slip Op. 02096 at 17-20.

As to the Frye inquiry, the court emphasized that while Frye focuses on principles and methodology and not conclusions, conclusions and methodology are “not entirely distinct from one another.” Id. at *16, quoting General Electric v. Joiner, 522 U.S. 136, 146 (1997). Thus, a trial court may reject the expert’s opinion if there is simply too great an analytical gap between the data and the opinion proffered. Id.

With this admonition in mind, the court concluded plaintiff’s expert’s testimony regarding the relied upon scientific literature, which he viewed as accepting his opinion of a causal connection between mold exposure and plaintiff’s alleged injuries, fell short of satisfying Frye’s requirement of “general acceptance.” The reason is that the cited literature only spoke in terms of “risk,” “linkage” and “association” and such relationships do not mean that there is a cause-effect relationship. Id. at *17-18.7 Thus, the expert did not apply generally accepted methodology in evaluating the pertinent facts.

Cornell clearly instructs the trial court that in applying the Frye standard it must closely scrutinize the relevant scientific literature and determine whether such literature in fact “generally accepts” the expert’s methodology and not just that the literature provides some support for the methodology. More certainty is required. Otherwise, the expert opinion will be rejected as failing the Frye standard.

As to the Parker inquiry, the court stressed the importance of identifying the cause of a plaintiff’s illness and how that cause was then capable of causing that illness, all within the framework of plaintiff’s relied upon methodology. Id. at *18-19. Here, where the claimed cause of plaintiff’s condition was exposure to mold, it was incumbent upon the plaintiff to show she was exposed to “levels of that agent that are shown to cause the kind of harm that plaintiff claims to have suffered.” Id. at *19, quoting Wright v. Williamette, 91 F.3d 1105, 1107 (8th Cir. 1996).

In the absence of any quantification of plaintiff’s level of exposure to the mold and any refutation of defendants’ expert’s statement that the measurement of molds in plaintiff’s apartment were “of expected level and distribution for any average home” when compared to sampling studies, plaintiff’s expert sought to establish the requisite foundation through a differential diagnosis. While acknowledging that a differential diagnosis is a recognized methodology, the court rejected the performance of a differential diagnosis as a means to establish the requisite causal connection Parker foundation. The reason is that such methodology necessarily assumes the final remaining cause is capable of actually causing the injury, whereas Parker requires proof of such causation. Id. In any event, the court found the expert’s differential diagnosis to be flawed for several reasons. Id.

The court’s rejection of the performance of a differential diagnosis as a means to satisfy Parker is significant. The reason is that it shows the court is committed to a fact-based showing of specific causation to establish compliance with Parker.

Michael J. Hutter is a professor at Albany Law School, and is special counsel to Powers & Santola.


1. Michael Hoenig has devoted his Products Liability column to a discussion of Cornell, noting that it should be on a litigator’s “must read” list. (Hoenig, “Ruling on Mold Clarifies ‘Reliability’ Needed From Experts,” NYLJ, April 4, 2014, p. 3, col. 3).

2. Soon after this ruling, defendant 360 West 51st Street Corp. settled with plaintiff.

3. A methodology must be employed or otherwise the opinion will be summarily rejected. See, Romano v. Stanley, 90 N.Y.2d 444, 451-452 (1997).

4. People v. Wesley, 83 N.Y.2d 417, 422 (1994).

5. Parker, 7 N.Y.3d at 447.

6. Id., quoting People v. Wesley, 83 N.Y.2d at 429.

7. Of note, the court cited in support the federal court’s Reference Manual on Scientific Evidence.