JurisdictionNorth Carolina


Sometimes an expert is not needed because the jury can do perfectly well without one. To determine whether expertise is admissible, Rule 702 uses a helpfulness standard: Will the proffered expert testimony "help the trier of fact to understand the evidence or to determine a fact in issue?"

In explaining this standard, the federal drafters quoted Dean Ladd: "There is no more certain test for determining when experts may be used than the common sense inquiry whether the untrained layman would be qualified to determine intelligently and to the best possible degree the particular issue without enlightenment from those having a specialized understanding of the subject involved in the dispute."6 Rule 702 is also consistent with Wigmore's formulation of the test for expert testimony: "On this subject can a jury receive from this person appreciable help?"7

Rule 702's helpfulness standard is a more liberal formulation of the subject matter requirement than that found in many common-law opinions. The common law often phrased the requirement as whether the subject was beyond the comprehension ("ken") of lay persons.8 In short, Rule 702 rejects "necessity" as the appropriate test.9 The overlap between lay and expert testimony is discussed in the previous chapter.

There are some controversial issues here. For example, at one time virtually all the courts excluded expert testimony concerning the unreliability of eyewitness identifications because "the trustworthiness in general of eyewitness observations [is] not beyond the ken of the jurors."10 In State v. Chappie,11 however, the Arizona Supreme Court ruled that the trial judge erred in excluding such testimony. According to the court,

[e]ven assuming that jurors of ordinary education need no expert testimony to enlighten them to the danger of eyewitness identification, the offer of proof indicated that [the expert's] testimony would have informed the jury that there are many specific variables which affect the accuracy of identification and which apply to the facts of this case.12

These variables may include risks associated with cross-racial identifications, unconscious transference, the weak correlation between witness confidence and accuracy, and other factors.13

In contrast, police officer testimony on modus operandi was readily accepted. Testimony by police experts on the m.o. of various types of crimes, such as counterfeiting,14 bookmaking,15 pickpocketing,16 fraud,17 organized crime,18 and gang-related crimes,19 has been admitted. The most frequent use of this type of testimony involves drug trafficking. Expert testimony has been introduced on the operation of clandestine laboratories,20 the street value of drugs,21 the quantity of drugs that is consistent with distribution rather than personal use,22 strategies of deception,23 and other aspects of the drug trade.24 In addition, expert testimony on various tools of the drug trade, including beepers,25 code words,26 weapons,27 duct tape,28 and the like,29 has similarly been accepted.

There are, of course, limitations on this type of testimony. For example, United States v. Garcia30 involved the testimony of an FBI language specialist who translated ten telephone conversations and gave his opinion about the meaning of certain phrases used in the conversations. The specialist also testified that the phrase "your old man" referred to the defendant. The Tenth Circuit ruled this testimony improper: "Unlike [the expert's] opinion as to jargon used in the drug trade which may be explained by expert opinion testimony, . . . no specialized knowledge is necessary to understand the phrase 'your old man.' Therefore, expert testimony on this point was unnecessary."31

[A] Expert Opinion on Credibility

As stated by the Eighth Circuit, "expert testimony going to the issue of credibility is not admissible."32 This issue frequently surfaces in cases that admit rape trauma syndrome or child abuse accommodation syndrome. According to the First Circuit, "[r]ather than requiring the wholesale exclusion of expert testimony concerning credibility issues, these cases stand for the more limited proposition that an expert's opinion that another witness is lying or telling the truth is ordinarily inadmissible pursuant to Rule 702 because the opinion exceeds the scope of the expert's specialized knowledge and therefore merely informs the jury that it should reach a particular conclusion."33 The court went on to rule that expert psychiatric testimony that the defendant suffered from "pseudologia fantastica" that caused him to make grandiose statements similar in nature to the statements the prosecution was seeking to use against him was admissible under Rule 702.

[B] Expert Opinion on the Law

A recurring issue is whether an expert can testify "on the law," which would include expert opinion testimony applying a legal standard to the facts as well as expert testimony on some aspect of the substantive law. The prevailing rule prohibits such testimony.34 Some courts have recognized, however, that this issue is not as simple as might initially appear:

The question is this: when can expert witnesses offer legal opinions? In addressing this question, federal courts have not provided

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