Expert Testimony Essay

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Over time, the definition of an expert witness has evolved into someone who provides opinion testimony at trial based on specialized knowledge, training or experience, reliability, relevancy, and assistance in helping the fact finder to reach a decision. An expert witness should not be confused with a lay witness, however, who usually testifies to facts based on what they have observed or heard. Rather, an expert witness is defined not only by their unique qualifications but also by the nature of their admissible testimony, which must satisfy standards of reliability.

These criteria are further defined within the Federal Rules of Evidence (Rule 702), which is divided into four parts: qualifications, reliability, helpfulness, and foundation. Moreover, the proposed expert witness must be sufficiently qualified through formal training and education or practical experience to testify on the particular matters at issue. The opinion must be reliable according to the standards of the expert’s field. The opinion must be “helpful” to the fact finder—that is, the opinion must address matters relevant to the dispute that require expertise beyond the kind of ordinary lay jurors or the court. Finally, the opinion must be grounded in the type of data and information customarily relied upon by other experts in the particular field. While Rule 702 appears rather explicit, questions have emerged surrounding issues of confidentiality, loyalty, and personal integrity. These ethical concerns center on the following questions:

  • What are expectations of confidentiality regarding expert witnesses?
  • Where does the expert witness’s loyalty lie: with the court or with the client?
  • Should an expert knowingly present opinions or testimony that is false or misleading?
  • What can be said of an expert witness who can potentially testify for either the prosecution or the defense?
  • Should expert witnesses remain free from any financial inducements that might interfere with their honesty and impartiality?

These questions are controversial, but represent only a mere fraction of ethical concerns surrounding the role of expert witnesses. To appreciate the broader context and importance of these issues, it is necessary to understand a few facts about the history of expert witnesses.

Historical Background

Under common law, the courts frowned upon opinion testimony, feeling that jurors were fully capable of drawing their own inferences from factual evidence. Whenever a dispute required expert knowledge, courts would empanel jurors with special qualifications or seek the aid of skilled persons whose opinions the judge could adopt or reject. Through trial and error a third method evolved whereby a learned person could offer an opinion directly to the jury, though judges remained doubtful about the practice. The earliest known use of an expert witness in English law came in 1782 when a court, hearing litigation relating to the silting-up of Wells Harbour in Norfolk, accepted evidence from a leading civil engineer, John Smeaton. The court’s decision to accept Smeaton’s evidence is widely cited as the root of modern rules on expert evidence. However, the use of expert testimony was rare until 1957, when an English judge called on an expert witness to help establish the guilt of suspected serial killer Dr. John Bodkin Adams. By the late 18th century, the practice of using experts to offer opinion testimony was established.

From the beginning, the expertise of various witnesses reflected different disciplines and occupations, but none more common than medical and mental health professionals. The treason trial of Edward Oxford provides a good example. By examining the publications and documents of the testifying physicians as well as the legal literature, one discovers that the Oxford insanity trial of 1840 was a key moment in the development of the medical expert witness in Anglo-American law. This was the first trial that called on several physicians who had neither examined nor even seen the defendant until the night before the trial. Yet, they formed an unequivocal opinion about the existence of insanity and communicated this opinion to the jury directly, without reference to a hypothetical person. Because the expert’s ability to offer opinions rather than simply factual observations was a powerful influence in trials, definitional concerns paved the way for the enactment of formal rules of evidence to ensure that expert testimony was reliable enough to complement the fact finder’s task.

Ethical Obligations

The use and reliance on expert witnesses in both civil and criminal cases has continually grown and almost every major case involves the use of “dueling experts.” While the exact percentage of cases using expert witnesses is unknown, it is reasonable to conclude that they are more likely present than absent. Once contracted, most experts are expected to maintain a sense of integrity and honesty embodied by most professional codes of conduct. Their frequent hire and involvement in court cases, however, has not escaped the watchful eye of cynical observers who regard them as little more than “hired guns” or, even worse, “liars for hire.” These expressions convey an underlying tension between their responsibilities to their employer and their responsibilities to the court.

Regardless of whether the case is heard before an administrative tribunal or a court, expert witnesses are expected to present an impartial and objective opinion of the inferences to be drawn from the facts. Moreover, they are reminded that the central ethical obligation of an expert is “to tell the truth, the whole truth, and nothing but the truth,” rather than simply those aspects of the truth that benefit their client. This basic imperative is underscored in Federal Rule of Evidence 102, which implies that their loyalty rests with the courts in which their primary function is to assist judges and juries to make informed decisions. As such, they are expected to remain totally objective and committed to the truth irrespective of who has retained them. These ideals echo the sentimental voice of impartiality. When an expert witness places a client’s interests above the court’s interests it is conceivable that the long-term negative effect is that their expert opinions will have less value— even when honestly and fairly rendered.

Although many feel an expert witness’s obligation is to the courts, an opposing viewpoint suggests that the witness also has an ethical obligation to represent the interests of their clients. If some view this as conflicting and even unethical, the fault may be much more systemic as some advocate a broader approach to ethics that takes full account of all the forces affecting the court system. Since judges and lawyers are also known to engage in unethical behaviors, it is a fallacy to limit ethical thinking to the behavior of particular expert witnesses in the courtroom.

A Code of Ethics

Beyond the culture of courtrooms, characterized by some as immoral and corrupt, ethical behavior should be judged by the standards of the discipline of the expert. In fact, a number of professional associations have promulgated codes of conduct that are consistent with this view. Regarding expert witnesses, any prospective code should address issues of confidentiality, conflicts of interest, and professionalism, among others. Regarding objectivity, for instance, clients are reminded that a party to any legal proceeding who seeks to proffer expert testimony to serve its own purposes must remain aware of the obligations objectivity imposes, both on the expert and the party who retains him or her. Barring the creation of such codes, some suggest that one way to alter the perception and practices of partial expert witnesses (as “guns for hire”) is to make greater use of court-appointed experts. This would negate their working for either the defense or prosecution (and litigants). Those who hold strongly to this view may conclude that since truth is so elusive, the primary purpose of trials is not seeking the truth, but rather some other objective such as the peaceful resolution of conflict or achieving procedural justice.

Serious questions remain about the role of expert testimony. For example, can professional integrity be maintained by experts who take every case they are offered? Does a conflict of interest exist if, after meeting with the litigant, the expert is subsequently retained by the defense? To what extent are expert witnesses bound by the rules of confidentiality regarding a former client?


  1. Cullen, Pamela V. A Stranger in Blood: The Case Files on Dr. John Bodkin Adams. London: Elliott & Thompson, 2006.
  2. Hand, Learned. “Historical and Practical Considerations Regarding Expert Testimony.” Harvard Law Review, v.15/1 (1901). (Accessed March 2013).
  3. Sanders, Joseph. “Expert Witness Ethics.” Fordham Law Review, v.76 (2007). (Accessed March 2013).

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