Experts and their Gatekeepers

Experts and their Gatekeepers

Adapted from Yannacone’s featured presentation on 12 October 2000, at the NYSBA CLE Program, Winning Your Case at the Deposition: Effective Tools for the Successful Litigator, co-sponsored by the Torts, Insurance and Compensation Law Section and the Committee on Continuing Legal Education of the New York State Bar Association. [full text with in-line citations]

Just who is an Expert?

Basically an expert is someone who knows a great deal about something of interest to you or your client. On a more practical level, an expert is anyone who knows more about something you should know about than you do.
The precise legal definition of an expert is only of value when opinion testimony is critical to your case. Nevertheless, the strict definition of expert contained in the Federal Rules has to be on your mind at all times during the course of litigation.
If you do not want the expert witness to testify as an expert, then you must establish that the body of knowledge upon which the expert wishes.to base their expert opinion is not so complicated as to be beyond the understanding of the judge or the jury.
On the other hand, if you desperately need the expert witness to give an opinion favorable to position of your client, then your objective during the deposition is to establish, as convincingly as possible, that the body of knowledge upon which the expert opinion is based is so arcane and specialized that any judge or jurors who do not share the same background and credentials as the expert witness cannot be expected to understand the subject about which the expert is offering an opinion.
With the Discovery Channels, the Learning Channels, the Tuesday Science Supplements in most daily newspapers of large circulation, and the constant stream of magazine articles about science, medicine and technology, not to mention economics, business practices, antitrust law, and countless other topics, jurors, and even judges, are considerably more knowledgeable about technical issues today than in the past era when the Federal Rules of Civil Procedure were drafted and where laypeople were presumed to know much less than those with more extensive formal education.
Even in 1980, it was quite possible to explain the electron transport system and oxidative phosphorylation in cytochrome P450 enzyme reactions to a federal judge without the aid of an expert witness. And today, according to several reports on the judiciary, judges are even more knowledgeable.
The question of expertise is vexing. It must be resolved on a witness-by-witness basis through investigation and deposition. Nevertheless, the decision of whether a witness is an expert or not must, in the first instance, be made by the attorney presenting the witness as an expert and the attorney challenging the designation of the witness as an expert.

Daubert Did It!

In three cases decided in the 1990s [Daubert v, Merrell Dow Pharmaceuticals, 509 U.S. 579, (1993); General Electric Co. v. Joiner, 522 U.S. 136 (1997), Kumho Tire Co., Ltd. v. Carmichael, 19 S. Ct 1167 (1999).], the Supreme Court of the United States greatly expanded the discretion of trial judges to reject expert testimony. This “Expert Trilogy” imposed an obligation on trial judges to screen all expert witness testimony and to refuse to accept, acknowledge or permit a jury to hear testimony from experts who offer opinions that are unreliable or not considered helpful.
The first case in the trilogy, Daubert v. Merrell Dow Pharmaceuticals, established the gatekeeper obligation and applied it to science-based expert testimony. In the second case, General Electric Co. v. Joiner, the Court made clear that trial courts, not appellate courts, stand at the gate. Finally, in the third case, Kumho Tire Co., Ltd. v. Carmichael the Court expanded the gatekeeper role to include all proposed expert testimony, not just scientific testimony.
The appellate court in Joiner adopted this stringent standard of review because it perceived an implicit preference in the Federal Rules of Evidence for admitting expert testimony regardless of its scientific merit.
In his partial dissent in Daubert, Chief Justice Rehnquist set the stage for the third case in the trilogy when he asked whether the standard offered by the majority would apply to “an expert seeking to testify on the basis of ‘technical or other specialized knowledge’—the other types of expert knowledge to which Rule 702 applies—or are the ‘general observations’ limited only to ‘scientific’ knowledge?” The question remained unanswered until the Supreme Court decided Kumho Tire.
In Kumho Tire, plaintiffs alleged that a defect in a tire made and distributed by defendants caused the accident and proffered testimony from an expert on tire failure who examined the tire and opined that a manufacturer’s defect caused the blowout.
Even though the testimony was not based upon scientific knowledge, the trial court conducted a Daubert analysis and held that the testimony of plaintiffs’ expert was not admissible.
Applying the de novo standard, the Eleventh Circuit reversed the trial court’s conclusion of law that Daubert applied to the expert testimony at issue, holding that the Daubert analysis did not apply to testimony that was not based upon “scientific principles,” but only upon “skill- or experience-based observation.”
The Supreme Court reversed, holding that the “gatekeeping obligation” assigned to trial courts in Daubert applies to all types of expert testimony.

The Gates

Expert testimony is admissible only if it can pass through a number of “gates.” Five of these gates are an outgrowth of Daubert and are intended to ensure that the expert opinion is reliable because the knowledge of the expert is reliable. Reliability requires an examination of the methods and procedures used by the expert to reach an opinion, the data and assumptions relied upon by the expert as the basis for the opinion, and the reasoning process used by the expert to reach that opinion all in the context of the litigation in which the expert opinion is being offered.
Daubert set forth a non-exclusive checklist for trial courts to use in assessing the reliability of scientific expert testimony and Kumho extended application of the checklist to all expert testimony. The specific Daubert factors are

  • whether the technique or theory relied upon by the expert witness can be or has been tested; whether the hypotheses of the theory upon which the opinion is based can be challenged in some objective sense, or whether it is simply a subjective conclusion that cannot reasonably be tested
  • whether the technique or theory has been subject to peer review and publication
  • the known or potential rate of error of the technique .or theory when applied
  • the existence and maintenance of standards and controls; and
  • whether the technique or theory has been generally accepted in the scientific community.
“Knowledge” characterizes an expert

The Daubert/Joiner/Kumho trilogy clearly indicates that the Supreme Court of the United States gives great deference to the Federal Rules of Evidence, particularly Rule 702, in any consideration of expert testimony. The Rule 702 requirement of expert “knowledge” is the basis for the reliability inquiry called for by Daubert.
In Kumho Tire, as it had in Daubert, The Court noted that Rule 702 considered at least three types of expert testimony, “scientific, technical or other specialized knowledge,” and that the rule made no “relevant distinction” among them. The critical word in Rule 702 for purposes of the Daubert analysis is “knowledge,” not the words which modify or characterize “knowledge.”
The “testimonial latitude” granted to expert witnesses under the Federal Rules of Evidence is not limited to those witnesses who offer testimony based upon scientific principles. The Court said, “it would prove difficult, if not impossible, for judges to administer evidentiary rules under which a gatekeeping obligation depended upon a distinction between ‘scientific’ knowledge and ‘technical’ or ‘other specialized’ knowledge. There is no clear line that divides one from the others.” The general principles for evaluating expert opinion set forth in Daubert apply to all the expert matters described in Rule 702.
The obligation for trial courts after Kumho Tire is to determine “whether the testimony has a ‘reliable basis in the knowledge and experience of [the relevant] discipline’.” The discretion of the trial court is, in the words of Mr. Justice Scalia, “the discretion to choose among reasonable means of excluding expertise that is false and science that is junky. Though, . . . the Daubert factors are not holy writ, in a particular case the failure to apply one or another of them may be unreasonable, and hence an abuse of discretion.”
Both Joiner and Kumho Tire clearly dictate that the deposition of any putative expert witness must inquire, in great and searching detail, about the “methods and procedures” of the relevant scientific, technical or professional disciplines upon which the proffered expert opinion is based.
Each and every relevant method and procedure must be identified and a clear and convincing relationship between the methods and procedures and the expert opinion established based on a well-defined path from the methods and procedures to the expert opinion. In Kumho Tire, the plaintiffs’ expert’s opinion was inconsistent with the methodology he purported to follow. In Joiner, the expert purported to rely upon animal studies to support his conclusion. The court however, concluded that “there [was] simply too great an analytical gap between the data and the opinion proffered” for the opinion to be properly considered grounded in the methods and procedures of science.
The deposition of an expert witness must leave no question about whether the expert opinion satisfies the Daubert requirement of “knowledge” under Rule 702. The opinion must be something more than subjective belief or unsupported speculation. This requires the trial judge to determine “whether the reasoning or methods and procedures underlying the testimony are scientifically valid.”
If the issue is causation, the inquiry must address first the question of general causation “Can the putative cause produce or account for the observed effect?” then move to the question of cause-in-fact, “Did the putative cause contribute to the observed effect? How? By what means? At what time scale?” before even approaching the question of proximate cause.
Courts generally insist that an expert may not give opinion testimony to a jury regarding causation without demonstrating that the opinion was reached by some process of differential diagnosis, differential analysis or some other form of expert discrimination among alternatives which reliably eliminates other possible causes or at least establishes their probability ranking as possible causes.
Failure by an expert to meaningfully rule out or consider any multiple, well-recognized, potential causes for an observed effect is contrary to accepted methodology in any recognized science, profession, or trade which might form the basis for an admissible expert opinion. In Daubert, the proffered expert offered no tested or testable theory to explain how, from the limited information available to him, he was able to eliminate other potential causes of birth defects.

What kind of knowledge? Reliable knowledge.

The “reliability” of a scientific fact derived from a scientific principle generally depends on a number of factors common to the philosophy underlying the “scientific method” since the time of Francis Bacon.

  • the reliability of the underlying scientific principle
  • the reliability of the technique or process that applies the principle
  • the nature and condition of any instrumentation used in the process
  • adherence to proper procedures
  • the qualifications of the person who performs the test; and
  • the qualifications of the person who interprets the results.

The Daubert dilemma

The Daubert/Joiner/Kumho rules seem to use at least two meanings of the word, “reliable,” at the same time.
In certain contexts, “reliable” seems to mean that the explanative theory actually produces a correct, accurate, truthful, or valid conclusion. In other contexts, “reliable” means meriting confidence worthy of dependence or reliance, possessing sufficient assurance of correctness to warrant acceptance by the trier of fact-the dictionary definition.
In the Daubert discussion of “gatekeeping,” the Court seems interested in whether the proffered explanative theory actually produces a correct, accurate, truthful, or valid conclusion. The Supreme Court even expresses its confidence that federal judges can make a “preliminary assessment of whether the reasoning and methodology underlying the testimony is scientifically valid.”
The Supreme Court established as a rule of law that “evidentiary reliability will be based upon scientific validity,” and reaffirmed the basic premise of Rule 702 which requires that an “expert’s opinion will have a reliable basis in the knowledge and experience of his discipline,” which is a reference to general acceptance and sufficient assurances, the dictionary meaning of “reliable.”

The “Explanatory Theory” and “Knowledge”

Under Rule 104(a), whenever an expert proposes to testify about scientific knowledge in order to assist the trier of fact to understand or determine a fact in issue, there must be a preliminary determination that the reasoning, methods and procedures of the expert can be properly applied to the facts at issue in the litigation.
While declining to set out a definitive checklist or test, the Supreme Court in Daubert did identify factors that will assist the trier of fact to determine whether a theory, technique, reasoning, methodology, &c., collectively referred to as an “explanative theory,” represents scientific knowledge. The Supreme Court suggested that a key question is whether the theory or technique can be, and has been, tested, recognizing that, “Scientific methodology today is based on generating hypotheses and testing them to see if they can be falsified; indeed, this methodology is what distinguishes science from other fields of human inquiry.”
The Supreme Court then suggested that another important consideration is peer review, but expressly noted that, “Publication . . . does not necessarily correlate with reliability, and in some instances well-grounded but innovative theories will not have been published. Some propositions, moreover, are too particular, too new, or of too limited interest to be published. But submission to the scrutiny of the scientific community is a component of ‘good science,’ in part because it increases the likelihood that substantive flaws in methodology will be detected. The fact of publication (or lack thereof) in a peer-reviewed journal thus will be a relevant, though not dispositive, consideration in assessing the scientific validity of a particular technique or methodology on which an opinion is premised.
The third factor suggested is the known or potential rate of error, while the fourth factor is the existence and maintenance of standards controlling the technique’s operation.
The fifth and final factor, “General Acceptance,” had to be more subtly developed by the Supreme Court since it was expressly overruling the Frye decision.

Frye Revisited

Although a reliability assessment does not require, as it once did under Frye, explicit identification of a relevant scientific community and an express determination of the particular degree of acceptance of the expert opinion within that community, nevertheless, it does permit, and even encourages, such consideration. A technique that has been able to attract only minimal support within the scientific, technical or professional community of which the expert witness is a part may properly be viewed with skepticism. What general acceptance can provide for evidence and opinion testimony is “Sufficient Assurances of Correctness.”
Ordinarily, sufficient assurances of correctness can be established by showing the explanative theory, as applied, has gained widespread acceptance in the particular field to which it belongs. For certain methods and procedures, widespread acceptance is a sufficient alternative test. [A classic example would be well-established procedures in analytical chemistry. “All the chemical testing took place at a FDA laboratory, where analysts performed four procedures—Fourier transform infrared spectrometry, gas chromatography/mass spectrometry, high performance liquid chromatography and electrospray liquid chromatography tandem mass spectrometry. Each of these procedures reveals a substance’s ‘spectrum’ or ‘fragmentation pattern’—a sort of chemical fingerprint. Analysts then identify a substance by comparing its spectrum with spectra from known standard samples or from a computer library. These procedures, and the tools used to perform them, are widely used and generally accepted. in the fields of analytical and forensic chemistry.”
And another from economics, “Plaintiffs have amply demonstrated the soundness of the Cournot model as a fundamental, time-tested economic tool that has been widely accepted. for years by reputable economists. Indeed, the Cournot model provides the theoretical underpinnings for the Department of Justice’s Horizontal Merger Guidelines and the widely used Herfindahl-Hirschman Index (the ‘HHI’).” Of course, reliance on “widespread acceptance” is subject to the limitation that the entire field to which the explanative theory belongs may lack reliability. “[T]he presence of Daubert’s general acceptance factor [does not] help show that an expert’s testimony is reliable where the discipline itself lacks reliability, as, for example, do theories grounded in any so-called generally accepted principles of astrology or necromancy.”
In the alternative, the explanative theory can be shown to possess sufficient assurances of correctness by proof that the explanative theory, as actually applied, possesses particularized earmarks of trustworthiness.
Generally speaking, particularized earmarks of trustworthiness can be established if the explanative theory is shown to have been derived and employed in a manner consistent with processes customarily employed by experts in the particular field and
• meets the same standards for intellectual rigor demanded in the expert’s regular business and professional work
• conforms to applicable professional standards employed outside the courtroom, and
• is soundly grounded in the principles and methodology of the particular field.
The Supreme Court was interested in the general question of whether development of the explanative theory exhibits the aura of proper scientific methodology and that the expert, whether basing testimony upon professional studies or personal experience employs in the courtroom the same level of intellectual rigor that characterizes the practice of the expert in the relevant field.
Focusing on whether the explanative theory possesses the aura of proper scientific methodology rather than requiring the trial judge to decide whether the explanative theory in fact is true and correct comports with the Supreme Court’s observation in Daubert that “vigorous cross-examination, presentation of contrary evidence, and careful instruction on the burden of proof are the traditional and appropriate means of attacking shaky but admissible evidence.”
Daubert does not require that a party who proffers expert testimony to carry the burden of proving to the judge that the expert opinion is correct. As long as the expert’s testimony rests upon “good grounds, based on what is known,” it should be tested by the adversary process—vigorous cross-examination and competing expert testimony rather than excluded from jurors’ scrutiny for fear that they will not grasp its complexities or satisfactorily weigh its inadequacies.
Daubert neither requires nor empowers trial courts to determine which of several competing scientific theories is “correct.” Daubert and its progeny only require the party offering the evidence show that the expert opinion has been arrived at in a scientifically sound and methodologically reliable fashion.
Case law interpreting Daubert has established that, when evaluating the admissibility of expert testimony, a trial judge must first consider whether the testimony is consistent with the scientific method and not mere subjective belief or unsupported speculation; then determine whether the evidence or testimony assists the trier of fact in understanding the evidence or in determining a fact in issue.
An expert opinion should at least have a reliable basis in the knowledge and experience of the particular discipline involved.
The true spirit of the Supreme Court opinion in Daubert is found in the general instruction that the inquiry envisioned by Rule 702 is a flexible one. Its overarching subject is the scientific validity—and thus the evidentiary relevance and reliability–of the principles that underlie a proposed submission. The focus, of course, must be solely on principles and methodology, not on the conclusions that they generate. However, in Joiner, the Supreme Court was forced to acknowledge that “conclusions and methodology are not entirely distinct from one another.”

Probative value of expert testimony

Once the first requirement in Rule, 702 has been addressed and it has been established that the expert has “knowledge” and the expert opinion is based upon ”reliable” knowledge, there remains the question of whether the expert testimony will assist the trier of fact. The real test, and the foundation for the deposition strategy, is not whether the expert opinion is important to the determination of the case, but whether the expert testimony in support of that opinion will assist the judge and jury in resolving issues.
Even if expert testimony is sufficiently reliable and helpful to satisfy Rule 702, it may still be excluded under Rule 403, “if its probative value is substantially outweighed by the danger of unfair prejudice, confusion of the issues or misleading the jury. … Expert evidence can be both powerful and quite misleading because of the difficulty in evaluating it. Because of this risk, the judge in weighing possible prejudice against probative force under Rule 403 of the present rules exercises more control over experts than over lay witnesses.”
Expert testimony under Rule 702 is also subject to other rules.
Rule 703 provides that expert opinions based on otherwise inadmissible hearsay are to be admitted only if the facts or data which might otherwise be excluded as “hearsay,” are “of a type reasonably relied upon by experts in the particular field in forming opinions or inferences upon the subject.”
Rule 706 allows the court, at its discretion, to obtain the assistance of an expert of its own choosing. This practice is becoming more prevalent as cases become more complex and dockets more congested.
Try to identify the relationships, business and professional, and even personal or collegial, between the expert testifying and the other “acknowledged” experts in the field.
It can be critically important, particularly in toxic substance, intellectual property, and economic interest cases, to identify the universe of potential “706 Experts,” and their relationships with the experts chosen by the parties to the litigation, long before the time arrives for the judge to select one from that universe

Rule 104(A) considerations

The burden of proof for preliminary determination of whether expert opinions are admissible is the same as the burden for all other preliminary determinations and is established by Rule 104(a). “In reaching a determination pursuant to Rule 104(a) on a question of admissibility, the court generally applies the standard for the burden of persuasion applicable in civil cases, more probably true than not true.
However, the Dauber/Joiner/Kumho Rules have significantly complicated Rule 104(a) determinations and consequently made Rule 104(a) hearings and the depositions upon which many of them are based much more important.
During a Rule 104(a) hearing, it is important to distinguish between support for the reliability of the opm1on and support for the reasonableness of reliance by the expert on what might be otherwise inadmissible hearsay evidence. Methodological and foundational reliability may be proven without reference to whether the expert knows or is aware of material in the record. Expert opinions may be based upon inadmissible data or facts “of a type reasonably relied upon by experts in the particular field in forming opinions or inferences upon the subject,” but the court must determine the reasonableness of the expert’s reliance in the context of the litigation about which the expert witness intends to testify.
Although Dauber clearly established that admissibility “should be established by a preponderance of proof,” Daubert did not identify the party with the burden of proof. Subsequently, lower courts have interpreted the opinion as placing the burden on the proponent to show that the evidence is admissible by a preponderance of the evidence.

”Admissibility” and “Sufficiency”

The several Courts who heard the Daubert case struggled with the distinction between the admissibility and the sufficiency of expert evidence. The district court focused on the insufficiency of the evidence.
The Ninth Circuit in its first opinion stressed the inadmissibility of the evidence. The Supreme Court noted that the evidence might be admissible under the Daubert factors but still be insufficient, thus permitting a summary judgment or directed verdict.
“Admissibility” and “sufficiency” of scientific evidence necessitate different inquiries and involve different stakes. Admissibility entails a limited threshold inquiry over whether certain piece of evidence ought to be admitted at trial, while a sufficiency inquiry, which asks whether the collective weight of a litigant’s evidence is adequate to present a jury question, lies further down the road toward a verdict or decision on a motion for summary judgment.
Some authorities have interpreted Daubert as establishing two independent tests of expert opinion, one for admissibility and another for sufficiency. Under this view, a court may sidestep an admissibility analysis when it is prepared to terminate the case on sufficiency grounds. Daubert does not directly address the issue, although it does indicate that summary judgment may be granted or a directed verdict entered when the evidence is insufficient to reach the fact finder, even though the evidence is admissible.
The dispute over whether Daubert applies to sufficiency review is more apparent than real. A judge who does not want to intrude on sufficiency questions has enough discretion under Daubert to exclude suspect expert testimony on admissibility grounds.
One important difference, however, is the standard of review used by an appellate court. A court that strikes expert evidence as inadmissible will have its judgment reviewed under the favorable “abuse of discretion” standard.
To be admissible, expert testimony need not directly address or prove an ultimate dispositive issue; it need only provide evidence for a proposition that is part of the proof of the ultimate issue. An expert’s “data and testimony need not prove the plaintiffs’ case by themselves; they must merely constitute one piece of the puzzle that the plaintiffs endeavor to assemble before the jury.
If an expert opinion is based upon a foundation of data from other experts, each item of data may be admissible as one “brick in the wall” establishing the reliability of the a party’s theory of the case. However, if all of the admissible pieces of evidence do not establish a reliable and substantial foundation for the expert opinion, the opinion is inadmissible. .
In complex cases where a great deal of seemingly unrelated data is required to establish the foundation for an expert opinion, the evidence establishing the individual elements of the case can initially be admitted through a finding of conditional relevancy under Rule 104(b).
Data may be admissible as part of the proof of an element of a claim, but it may still be legally insufficient evidence to support a judgment or verdict. A common example is where the only evidence to support a finding of causation in a toxic tort case is one or a small series of anecdotal case studies. While admissible, those limited studies, standing alone, are usually insufficient to establish causation.
However, temporal proximity between an injury and a chemical exposure can be used as “confirmatory data.”