Expert Witnesses, Adversarial Bias, and the (Partial) Failure of theDaubert Revolution

• Position: David E. Bernstein: Professor, George Mason University School of Law
• Pages: 02

David E. Bernstein: Professor, George Mason University School of Law. The author thanks the George Mason University Law and Economics Center for providing funding for this Article. Joe Cecil, Ed Cheng, Carl Cranor, David Crump, George Gies, Sam Gross, David Kaye, John Langbein, Michael Risinger, and Chris Sanchirico provided helpful comments, as did participants in faculty workshops at Brooklyn Law School and the University of Michigan Law School.

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I Introduction

The American judiciary traditionally had a laissez-faire approach toward the admissibility of most categories of expert testimony.¹ This approach ended in federal courts when the U.S. Supreme Court adopted a reliability test for the admissibility of expert testimony in a series of three decisions beginning with Daubert v. Merrell Dow Pharmaceuticals, Inc.² An amendment to Federal Rule of Evidence 702 then codified a stringent interpretation of the "Daubert trilogy."³ Many states also have adopted some version of the Daubert reliability test.⁴ Given that expert testimony is crucial to modern civil and criminal litigation, the emergence of the Daubert-702 reliability test for expert testimony is likely the most radical, sudden, and consequential change in the modern history of the law of evidence.

Despite the sweeping changes wrought by the Daubert trilogy, the Supreme Court never explained what implicit policy considerations motivated its decision to reverse generations of judicial practice. Instead, the Court relied on solely a wooden, literal interpretation of the then-extant version of Federal Rule of Evidence 702.⁵ In turn, the Federal Rules Advisory Committee, in amending Rule 702 to codify the trilogy, simply relied on the Supreme Court's opinions. The Committee provided no independent justification for the new rule.⁶

The failure to explicate the logic behind Daubert and its progeny has left the reliability test vulnerable to persistent criticism.⁷ Daubert critics point out Page 453 that no special reliability test applies to other categories of often unreliable testimony, such as eyewitness testimony.⁸ They argue that a reliability test is equally inappropriate for expert testimony.⁹

This Article contends that the implicit rationale for the modern special rules for expert testimony is that such testimony is uniquely vulnerable to "adversarial bias."¹⁰ Adversarial bias refers to witness bias that arises because a party to an adversarial proceeding retains experts to advance its cause.¹¹

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Adversarial bias has at least three sources: (1) conscious bias, (2) unconscious bias, and (3) selection bias.¹² The problem of conscious bias arises when "hired guns"¹³ adapt their opinions to the needs of the attorney Page 455 who hires them. Ordinary lay witnesses also can have conscious bias,¹⁴ but that problem is not as acute for several reasons. First, lay witnesses, unlike experts, are not paid for their testimony, which eliminates the possibility of serving as a "witness for hire." Second, lay witnesses are only permitted to present opinion testimony based on their own rational perceptions, limiting the scope of their testimony.¹⁵ Third, attorneys can shop from an almost unlimited pool of expert witnesses,¹⁶ while generally a very limited pool of potential ordinary fact witnesses exists in any given case.¹⁷ Finally, jurors may be particularly likely to assume that an expert witness, particularly a scientist, is an unbiased participant in the proceedings.¹⁸

Moreover, while it is often possible to discredit a lay witness by pointing out the source of her bias (such as a financial stake in the litigation or a relationship with a party), opposing counsel will inevitably find it extremely difficult to discredit a hired-gun expert for taking money for his testimony. After all, opposing counsel will have his own expert-who may be scrupulously honest and forthright-on his payroll.¹⁹ Therefore, opposing counsel will be unlikely to bring out the conscious bias of a hired gun effectively on cross-examination.

The second type of adversarial bias is unconscious bias. As Sir George Jessel pointed out in an English judicial opinion over a century ago, "Undoubtedly there is a natural bias to do something serviceable for those Page 456 who employ you and adequately remunerate you."²⁰ Unconscious bias exists across various categories of expertise,²¹ but it is an especially persistent and worrisome problem with regard to testimony by forensic scientists. Most forensic scientists work for government crime labs and are part of the prosecution team. Therefore, they naturally identify with the prosecutor's goal of convicting a particular defendant.

A forensic expert's unconscious bias can easily affect his conclusions,²²especially when these conclusions necessarily rely, as they often do, on subjective judgments.²³ Moreover, prosecutors are often responsible for evaluating forensic scientists' performances. This can lead to a desire, conscious or not, to reach conclusions that assist the prosecution.

The third type of adversarial bias is selection bias. Selection bias means that the experts retained by a party will not represent a random sampling of expert opinions. Rather, they will represent the perspective the attorney wants to present at trial. Sir Jessel noted many years ago that experts are selected "according as their opinion is known to incline."²⁴ As a result, the court does "not get fair professional opinion" from each party's experts, but "an exceptional opinion" from each side.²⁵

Assume, for example, that the key issue in a particular case is whether a particular painting is a genuine Picasso. Assume also that of the fifty qualified Picasso experts in the United States, forty-two would conclude that it was real and eight that it was counterfeit.

Even if the attorney for the "it's counterfeit" side chooses not to solicit a venal hired gun (or cannot find one), selection bias will allow this attorney to find several sincere, congenial experts from the sixteen percent who take that position.²⁶ The "it's genuine" side will counter with several sincere Page 457 experts of its own. The jury will receive a false sense that the issue is a very close one, when expert opinion actually overwhelmingly favors one side.²⁷

In some circumstances, the jury may not hear from any expert whose views represent mainstream expert opinion. For example, assume that the range of expert opinion regarding the appropriate amount of civil damages in a particular case is $100,000 to $800,000, with the median clustering around $350,000. Assuming that search costs are not prohibitive, the parties are likely to present testimony from experts who endorse figures close to $100,000 or $800,000, but none who support a figure close to $350,000.

If adversarial bias is the problem addressed by Daubert and Rule 702, the next question is whether the reliability test is a sound mechanism for reducing that bias. Amended Rule 702, codifying the Daubert trilogy, leaves the search for and selection of experts to the parties. It also retains the implicit assumption that expert witnesses primarily will be adversarial experts called and paid for by the parties. Thus, the Court and the Advisory Committee sought to retain the perceived advantages of the adversarial system.²⁸ Specifically, litigants have far more incentive to find a qualified, competent expert who can successfully challenge a preliminary conclusion Page 458 or the received (but incorrect) wisdom than will a judicial bureaucrat with no financial stake in the matter.²⁹

While retaining the adversarial system, Rule 702 tries to mitigate the consequences of adversarial bias by requiring district courts to exclude unreliable testimony. Expert testimony is admissible only when "(1) the testimony is based upon sufficient facts or data, (2) the testimony is the product of reliable principles and methods, and (3) the witness has applied the principles and methods reliably to the facts of the case."³⁰

Rule 702 and the Daubert trilogy thus attempt to alleviate the problem of adversarial bias by allowing attorneys the opportunity to challenge the other side's proffered expert testimony as unreliable.³¹ The question, however, is whether this solution is an adequate and appropriate response to the problem. This Article addresses this question in the context of three broad categories of expert evidence: forensic testimony in criminal cases, speculative causation testimony in toxic tort cases, and experience-based "connoisseur" testimony³² in all types of cases.

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In Part II, this Article concludes that the reliability test is not, by itself, an adequate solution to the problem of adversarial bias in forensic science; rather, a major overhaul of the forensic science system is needed. As for speculative causation and connoisseur testimony, discussed in Parts III and IV of this Article, respectively, Rule 702's reliability test is too restrictive. The rule requires the exclusion of virtually all such testimony, even when the testimony potentially could be useful to the trier of fact, because, as discussed below, such testimony never has objective indicia of reliability when provided by adversarial experts. Courts currently face two choices: they can faithfully apply Rule 702's dictates and entirely exclude potentially helpful categories of evidence or ignore or evade the strictures of Rule 702 and admit testimony not shown to be reliable. A better alternative would be for courts to appoint nonpartisan experts to advise them on the reliability of proffered testimony or perhaps even exclude adversarial experts and replace them with court-appointed experts. As discussed below, assuming appointed experts meet preliminary tests of competency, the nonpartisan stance of such...