- An expert witness is a person whose scientific, technical or other specialized knowledge, acquired through education, training, experience, or otherwise, can assist the trier of fact to understand the evidence or determine or determine a fact in issue.
- The court must determine whether the witness is qualified before allowing him or her to testify as an expert – if there is an objection, a voir dire examination may be necessary.
- If the witness is qualified as an expert, then he or she can testify in the form of an opinion, and may answer hypothetical questions related to his or her area of expertise.
Overview: Who/What Is an Expert Witness?
The most significant difference between ordinary lay witness testimony and expert opinion testimony is that a lay witness must have personal knowledge about the subject matter of his or her testimony (Rules 602 and 701), while an expert does not necessarily need to have personal knowledge, but must have the required expertise to render an opinion in the case (Rules 702 and 703). To be admissible, the testimony offered by the expert witness must be:
- Relevant to the case;
- Qualified by education, training, or experience;
- Reliable, per the three-prong reliability test of Rule 702(a) and Daubert v. Merrell Dow Pharmaceuticals, 509 U.S. 579 (1993); and
- Not excluded by some other applicable rule of evidence, such as Rule 403 (unfairly prejudicial).
An expert witness does not necessarily have to be “better educated” than the jury to give an opinion. As long as a witness has expertise acquired through specialized knowledge, skill, experience, training, or education, and those expertise will help the factfinder to understand the evidence or to determine an issue in the case, the witness may be qualified as an expert to give an opinion about that subject. See G.S. 8C-1, Rule 702; State v. Gainey, 355 N.C. 73 (2002) (“Expert testimony is properly admissible when the witness, because of his expertise, is in a better position to have an opinion on the matter than is the trier of fact.”). Although an expert usually does have a scientific or technical degree or license, a person can also be qualified as an expert witness if he or she has practical experience in a relevant subject area which would be helpful for understanding or deciding a particular issue. E.g., State v. Willis, 61 N.C. App. 23 (1983) (drug officer properly gave opinion about significance of papers found in defendant’s wallet); State v. Steelmon, 177 N.C. App. 127 (2006) (law enforcement officer properly testified on lividity of murder victim’s body and approximate time of death).
Conversely, there are limitations on offering expert opinion testimony about a matter when the jury is in just as good a position to determine the facts as the proposed expert. E.g., State v. Trent, 320 N.C. 610 (1987) (error to allow doctor to opine that he believed the victim was, in fact, “sexually abused” by defendant, when the physical evidence only showed that she had been sexually active at some point – “there is nothing in the record to support a conclusion that he was in a better position than the jury to determine whether the victim was sexually abused”); State v. Jackson, 320 N.C. 452 (1987) (error to allow expert to opine that defendant was “probably” the father of the child, based on evidence that showed the likelihood of paternity ranged from 93.4% to 99.91% - given the evidence before it, “the jury was in as good a position as Dr. McMahan to determine whether defendant was ‘probably’ the father of the victim's child”).
In reviewing a trial court’s decision regarding the admissibility of expert testimony, the appellate courts apply a deferential “abuse of discretion” standard. See, e.g., State v. Walston, 369 N.C. 547 (2017); State v. McGrady, 368 N.C. 880 (2016); State v. Babich, 252 N.C. App. 165 (2017); State v. Hunt, 249 N.C. App. 428 (2016).
Qualification of an Expert Witness
The party that seeks to introduce expert opinion testimony generally has the burden of proving the qualification of a witness, and the admissibility of the proposed testimony or evidence being offered. See State v. Ward, 364 N.C. 133 (2010). In many cases, this can be done with no interruption in the proceedings by simply asking the witness to explain his or her background, training, and qualifications as part of the direct examination. However, if the opposing party disputes the witness’s qualification, a voir dire hearing on the issue may be necessary.
A voir dire hearing is a preliminary examination of a witness, conducted outside the presence of the jury, to determine whether the witness is competent to testify as an expert, and whether his or her testimony is admissible as such. A voir dire hearing need not be conducted unless the opposing party enters a specific objection to the testimony or evidence. See Kenneth S. Broun, Brandis & Broun on North Carolina Evidence, § 16 (7th ed. 2011). Leading questions may be asked on voir dire because the rules of evidence are not applicable to the hearing (except for the rules concerning privileges). See G.S. 8C-1, Rule 104(a).
Practice makes imperfect
If the defense objects to the expert’s qualifications and the court conducts a voir dire hearing, the jury will not be present for it. If the objection is overruled and the witness is permitted to testify, some prosecutors may unconsciously rush or abbreviate their questions about the expert’s qualifications and experience the second time around (in front of the jury), since it feels like “we already did this.” Remember that the jurors need to hear all the details about the witness’s qualifications and experience, so that they can properly assess the expert’s credibility and give due weight to his or her testimony.
Qualifying an Expert Witness
- Qualification Issues and Questions
- Medical, technical, or scientific expert:
If the witness is a traditional medical, technical or scientific expert, he or she sould be questioned about the following:
- Occupation—how long
- Present position—title and duties
- Education and training—particularly in field of expertise
- Work background and experience—kind and length
- Licenses or certificates held
- Prior qualification(s) as an expert witness
- Experience, training, or practice expert:
If the witness is an expert based on practical experience (for example, a law enforcement officer testifying as an expert based on personal knowledge, in-service training, and field experience) he or she should be questioned about the following:
- Occupation or trade—how long
- Present job—name of employer, title and duties, and any specialty
- Education and training—particularly in the specialty
- How long witness has been working with these kind of cases
- How many times has the witness examined the type of evidence in issue
- Practical experience
- Medical, technical, or scientific expert:
More suggested questions
The list above provides general suggestions for the types of qualifying questions the prosecutor should ask. For a more structured outline and some additional suggested questions, see the related Expert Testimony entry entitled “Generic Question Outline.” Additionally, prosecutors should review the specific suggested questions contained in this resource guide for several of the most common areas of expertise (e.g., DNA, fingerprints, or drug identification). See the related entries on those subjects to review the questions.
- Tender witness as an expert:
After laying a proper foundation concerning the witness’s background and training to establish his or her expertise (and that the testimony would be helpful to the jury), the prosecutor should formally tender the witness to the court as an expert in a particular field. If the defense attorney does not object to the witness’s qualifications before the court finds the witness to be an expert, any later objection is waived. State v. Hunt, 305 N.C. 238 (1982). However, an initial proper objection to an expert’s qualifications continues to apply to any of the expert’s subsequent testimony without the need to repeat the objection. G.S. 15A-1446(d)(9).
Even though there is not a specific rule of evidence that the witness must be “formally” tendered as an expert to the court, the better practice is to do so. See State v. Wise, 326 N.C. 421 (1990) (no need for trial court to make formal ruling that witness was an expert because her qualifications had already been offered into evidence).
Presentation of Expert Testimony
In most cases, after establishing the witness’s qualifications and laying a proper foundation for the testimony (by having the witness describe his or her work in connection with the case, explain any testing done and any results, and so on), the witness will be asked to explain what his or her analysis shows or signifies. For example, the expert witness may express a conclusion that the defendant’s fingerprints correspond with the prints found at the scene of the crime, or explain the extremely high likelihood that DNA recovered from the victim’s body came from the defendant. Expert witnesses are given the flexibility to testify in the form of an opinion “or otherwise.” G.S. 8C-1, Rule 702(a). The witness's opinion may not be simply conjecture or speculation, but there are no “magic words” for how such an opinion has to specifically elicited or phrased. See, e.g., State v. Fullwood, 323 N.C. 371 (1988), vacated and remanded on other grounds, 494 U.S. 1022 (1990) (no error where state's expert in homicide trial testified about the estimated length of time between injuries and death, but noted that his estimate was "more or less a guess" - witness's testimony was "not regarded as being a mere conjecture or speculation but as a colloquial way of expressing an estimate or opinion").
“Do you have an opinion, satisfactory to yourself…”
There is no particular formula or phrasing that must be used by an expert witness when offering an opinion or conclusion, but by convention and practice (or simply because the jury expects it), the prosecutor’s question and the expert witness’s answer are often phrased in a somewhat formal and stylized manner.
For example, with a scientific or technical witness, the question and answer might be presented as follows: “Based on the testing and analysis you just described, do you have an opinion, to a reasonable degree of scientific certainty, as to the identity and nature of the white, powdery substance recovered from the defendant’s pocket?” (Yes, I do.) “And what is that opinion?” (The substance is cocaine.)
There is likewise no requirement that an expert must testify in response to “hypothetical questions,” see State v. Fearing, 304 N.C. 499 (1981), although hypothetical questions are permissible if they are within the witness’s area of expertise. See, e.g., State v. McCall, 162 N.C. App. 64 (2004) (relying on Rule 703 and State v. Wade, 296 N.C. 454 (1979), holding that trial judge did not err in allowing the state’s expert mental health witness to testify, in response to hypothetical questions and based on information related to her by third parties, that the victim’s behavior and characteristics were consistent with those of a child who had been sexually abused, even though the expert had not examined the child).
An expert witness is not prohibited from stating an opinion about an “ultimate issue to be decided by the trier of fact” in a case (for example, “in my opinion, yes, the defendant was the source of this DNA sample”), but an expert witness is prohibited from giving testimony involving legal conclusions (for example, “the defendant did not act with ‘premeditation and deliberation’”), or offering an opinion as to defendant’s ultimate guilt or innocence of the charged offense. See G.S. 8C-1, Rule 704; State v. Weeks, 322 N.C. 152 (1988); State v. Heath, 316 N.C. 337 (1986).
Pushing the envelope
Despite the prohibition against expressing an opinion on “legal conclusions” in the example above, in practice some experts may push the limits of this rule by testifying about the same general idea in slightly different words. The appellate courts have typically allowed some latitude in this area. See, e.g., State v. Mash, 328 N.C. 61 (1991) (trial court properly barred expert from opining on defendant’s ability to “premeditate and deliberate,” but did allow testimony about the defendant’s ability to “plan and scheme”).
The facts or data upon which an expert witness bases an opinion need not be independently admissible in evidence (see Rule 703), and the expert may testify as to his or her opinion without first testifying as to the underlying facts in support of that opinion, unless defense counsel requests such prior disclosure (see Rule 705). See also Delaware v. Fensterer, 474 U.S. 15 (1985) (admission of opinion testimony of prosecution’s expert witness who was unable to recall the basis for his opinion did not violate defendant’s Sixth Amendment right to confront witnesses against him).
Like other witnesses, an expert witness may use illustrative aids (photographs, animations, simulations, graphs, etc.) during his or her testimony to help illustrate and explain his or her testimony, as long as the illustrative aid is a fair and accurate representation of what it portrays. See State v. Carrilo, 149 N.C. App. 543 (2002) (allowing use of a video demonstrating a doll being shaken and animated diagrams of an infant’s brain to illustrate the expert’s testimony concerning the manner in which an infant is shaken to cause the severity of injuries sustained in the typical shaken baby syndrome case); see also State v. Harvey, 649 So.2d 783 (La. Ct. App. 1995) (allowing animation depicting state’s expert opinion of “how the shooting most likely occurred” and holding that the animations “enhanced the jury's understanding of the autopsy report and pictures as to the direction of the bullets and the position of the shooter”); People v. Hood, 62 Cal. Rptr.2d 137 (Cal. Ct. App. 1997) (similar ruling, finding that “the animation was illustrative, similar to an expert who draws on a board, and was not being introduced as evidence in and of itself, but only to illustrate the testimony of various prosecution experts”); State v. Farner, 66 S.W.3d 188 (Tenn. 2001) (allowing computer simulation of accident to “to explain and illustrate Officer Farmer's testimony about how the accident occurred”).
Defendant’s Statements Offered by a Defense Expert
Several appellate cases have upheld trial judges imposing limitations when a defense expert (typically, a mental health expert who has interviewed the defendant in the course of assessing him or her) seeks to testify regarding statements the defendant made to the expert about the alleged crime. Without such a limitation, the defendant could essentially use an expert witness as a surrogate to offer his testimony to the jury without exposing himself to cross-examination, distorting the protections of 5th Amendment and unfairly prejudicing the state. See State v. Harris, 338 N.C. 211 (1994) (defendant’s statements to defense psychiatric expert not admissible); State v. Baldwin, 330 N.C. 446 (1992) (defense expert psychologist could not testify about the substance of any self-serving, exculpatory statements made to him by the defendant unless or until the defendant testified about those statements); State v. Edwards, 174 N.C. App. 490 (2005) (trial court acted within its discretion in murder trial in excluding testimony of psychiatrist about conversations that he had with defendant, even though defendant argued that conversations formed basis for psychiatrist's expert opinion on defendant's mental state at time of crime, where the state did not choose to explore basis for psychiatrist's opinion); State v. Ballard, 127 N.C. App. 316 (1997), reversed on other grounds, 349 N.C. 286 (1998) (judge refused to allow psychologist to testify about the defendant’s hearsay statements to him explaining his version of the accident – prejudice to state outweighed any helpfulness to the jury).
By contrast, this rationale for exclusion does not apply when the state’s expert witness seeks to testify about any admissions made to him or her by the defendant, because such statements should be admissible as non-hearsay under Rule 801(d) (admission of party opponent) or, if applicable, under Rule 703 (basis of expert’s opinion).