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Federal Rules of Evidence and Experts: The Ultimate Guide

The Federal Rules of Evidence is a body of law that governs the admissibility of evidence in United States federal courts as well as in the states that have adopted the rules.

Anjelica Cappellino, J.D.

Written by
— Updated on April 11, 2022

Federal Rules of Evidence and Experts: The Ultimate Guide

Article VII of the Federal Rules of Evidence, comprised of six rules, covers the admissibility of expert witness testimony. An understanding of Article VII is critical for any lawyer seeking to introduce or exclude expert testimony at trial.

Rule 701 – Opinion Testimony By Lay Witnesses

The first rule in Article VII begins by defining expert testimony by what it is not – lay witness testimony. It states that if a witness is not testifying as an expert, opinion testimony must be: a) rationally based on the witness’s perception; b) helpful to clearly understanding the witness’s testimony or to determining a fact in issue; and c) not based on scientific, technical, or other specialized knowledge within the scope of Rule 702.

Subsection (a) requires first-hand knowledge or observation, while subsection (b) demands a lay witness opinion that is meaningful and carries more conviction than a broad assertion. Subsection (c) is a direct contrast to the definition of expert testimony in the subsequent rule. Under Rule 701, courts scrutinize lay opinions by determining whether the testimony is based on the witness’ own experience base and everyday reasoning. Lay opinions must rely on facts personally observed. The proponent of lay opinion testimony must provide the court not only with information establishing the witness’ personal knowledge, but must also show that the opinion is rationally related to those facts and is helpful to the jury. As discussed below, the admissibility of expert testimony is both different from and more lenient than that of lay opinions.

Rule 702 – Testimony By Expert Witnesses

Rule 702 is arguably the crux of Article VII, as it guides the court’s analysis in determining the admissibility of expert testimony. It states that an expert’s opinion is admissible if:

  1. the expert’s scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue
  2. the testimony is based on sufficient facts or data
  3. the testimony is the product of reliable principles and methods
  4. the expert has reliably applied the principles and methods to the facts of the case

The overarching aim of Rule 702 is to establish the relevance and reliability of the expert’s opinion. Rule 702 was amended in response to the seminal Supreme Court decision, Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993), which outlines a non-exhaustive list of factors for the courts to consider when determining the expert testimony admissibility. Although the specific Daubert factors are not codified in Rule 702, Rule 702 was amended broadly enough to allow consideration of any of the factors enumerated in Daubert and its progeny.

In consideration of Daubert’s holding that the court functions as a “gatekeeper,” Rule 702 grants wide judicial discretion in determining admissibility. Most importantly, the breadth of Rule 702, along with the case law that follows, establishes that exclusion of expert testimony is the exception rather than the rule.

Rule 703 – Bases of an Expert’s Opinion Testimony

Rule 703 establishes the bases on which experts may form their opinions. Notably, it allows experts to base their opinions on information that is inadmissible at trial. As Rule 703 states:

An expert may base an opinion on facts or data in the case that the expert has been made aware of or personally observed. If experts in the particular field would reasonably rely on those kinds of facts or data in forming an opinion on the subject, they need not be admissible for the opinion to be admitted. But if the facts or data would otherwise be inadmissible, the proponent of the opinion may disclose them to the jury only if their probative value in helping the jury evaluate the opinion substantially outweighs their prejudicial effect.

Under Rule 703, experts may base their opinions on inadmissible evidence so long as such information is reasonable to rely upon. In addition, the inadmissible evidence can only be disclosed to the jury if its helpful in aiding the jury’s understanding and its probative value substantially outweighs any prejudicial effect.

Inadmissible evidence in the context of Rule 703 usually relates to hearsay issues. However, Rule 703 is not limited to hearsay, as experts may also rely on information rendered inadmissible by the other rules of evidence and the Constitution. Inadmissible evidence relied upon by experts may be admitted for limited purposes; such as allowing the expert to reference the evidence only in general terms. Experts may be permitted to disclose inadmissible evidence to the jury for the limited purpose of evaluating the expert’s testimony, or in the alternative, the jury could use the evidence substantively.

Rule 704 – Opinion on an Ultimate Issue

Rule 704 allows the expert to testify as to the ultimate issue of fact; with the narrow exception that experts at a criminal trial may not testify as to whether a defendant had the requisite mental state to commit the charged offense. It is a response to older case law which limited an expert witness’s ability to testify as to the ultimate issues. The main purpose of Rule 704 is to assist the trier of fact. Therefore, an expert cannot render a conclusory opinion that prevents the jury from conducting their own analysis.

Rule 704 does not define what constitutes an “ultimate issue”. Case law has suggested that when a witness uses the same terms that are in a jury instruction, a line has been crossed (i.e., a medical expert stating a plaintiff’s condition as a “total permanent disability” in a personal injury suit or an accounting expert describing a failure to pay taxes as “willful” in a tax evasion case.). Because Rule 704 does not restrict opinions on the ultimate issues, experts are free to reach their own conclusions. They are also free to express their opinions without unnecessary semantic limitations.

Rule 705 – Disclosing the Facts or Data Underlying an Expert’s Opinion

Rule 705 discusses the form in which an expert may present its testimony. Under Rule 705, an expert may state an opinion without “first testifying to the underlying facts or data”. On cross-examination, the opposing party may inquire into the basis of the expert’s opinion. Rule 705, like 703, broadened previously followed common law rules by allowing experts to rely on information that would be otherwise inadmissible at trial and undisclosed to a jury.

There are obvious benefits to nondisclosure of facts and data, as it allows the experts to rely on a greater breadth of information. In certain instances, however, disclosing such facts and data may be advantageous to one’s case. If the material relied upon by the expert is helpful to understanding the issues at trial and can be easily presented to a jury, disclosure may not only assist the trier of fact in rendering a decision. It may also bolster the expert’s credibility by taking the opportunity to more effectively testify.

Rule 706 – Court-Appointed Expert Witnesses

Rule 706 governs court-appointed expert witnesses and permits courts to unilaterally choose an expert on its own. The court-appointed expert is required to advise all parties of its findings. They may be deposed, cross-examined, and called to testify by any party.

Although rarely invoked, Rule 706 ensures that, even if both parties elect not to produce an expert, expert testimony can still be elicited in matters in which the courts are dependent on expert guidance for deciding material facts. Proponents of court-appointed expert witnesses note that such appointments may ameliorate potential expert partisanship and “break through the log-jam of diametrically opposite viewpoints” between the parties’ own experts. However, courts have often viewed the appointment of experts as an extraordinary measure; only used when the traditional adversarial process is unable to properly elicit expert testimony that aids the trier of fact.

Overall, Article VII of the Federal Rules of Evidence lays the foundation for understanding the evidentiary rules of expert witness testimony. Taken together, the Rules highlight the significant role that expert witnesses play in the context of litigation.

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