Rule 702 Testimony by Experts

• Jurisdiction: Arizona

If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise.

Comment

This rule has two requirements for admission of expert opinion testimony: (1) the witness must be qualified as an expert, and (2) the offered specialized knowledge must assist the trier-of-fact to understand the evidence or determine a fact. The Arizona Supreme Court has held under Rules 702, 703, and 403 that expert testimony must (1) come from a qualified expert, (2) aid the trier-of-fact in evaluating and understanding matters not within their common experience, (3) be reliable, and (4) have probative value that outweighs its prejudicial effect.[1] Parts (1) and (2) come from Rule 702, and part (4) comes from Rule 403, which applies to all relevant evidence. Part (3), that the expert testimony be reliable, does not specifically appear in any of the three cited rules, although it is arguably a component of Rule 403, weighing the probative value against the prejudicial effect. It would appear that reliability of the testimony is more a question of the weight rather than the admissibility, and thus would be for the jurors rather than the trial court to decide.

Certain other Arizona cases have applied a different four-part test: (1) whether the expert is qualified, (2) whether the testimony is a proper subject for expert testimony, (3) whether the testimony conforms to a generally accepted scientific explanatory theory, and (4) whether probative value outweighs prejudicial effect.[2] Parts (1) and (2) come from Rule 702, and part (4) comes from Rule 403, which applies to all relevant evidence. Part (3) is based on Frye v. United States,[3] which holds that expert testimony deduced from scientific principles will be admitted only when the principle from which the deduction is made is sufficiently established to have gained general acceptance in the particular field in which it belongs. Rule 702 remains the test for admission of expert testimony in Arizona, subject as always to the discretion of the trial court to exclude such evidence under Rule 403. The third requirement, or Frye test, is limited to instances when a party seeks to introduce evidence based upon scientific principle, theory, or discovery,[4] and does not apply to expert testimony in general.[5]

Expert opinion testimony is admissible if it will assist the trier-of-fact to understand the evidence or to determine a fact in issue,[6] thus when a matter is of such common knowledge that a lay person could reach as intelligent a conclusion as an expert, the trial court should preclude expert opinion. A witness may qualify as an expert on the basis of knowledge and experience,[7] or training and education,[8] and the witness's specialty affects the weight of the testimony and not its admissibility, thus the witness does not necessarily need to have the same specialty as the area that is the subject of the litigation.[9] To qualify as an expert, a witness need not have the highest possible qualifications or highest degree of skill or knowledge; all the witness need have is a skill or knowledge superior to that of persons in general, and the level of skill or knowledge affects the weight of the testimony and not its admissibility.[10] Once the trial court determines that the witness qualifies as an expert, the trial court should not declare in front of the jurors that the witness so qualifies because this may give the appearance that the trial court is endorsing that witness's testimony.[11]

An accurate factual basis is a necessary element of a legally sufficient opinion,[12] and ambiguities about the factual basis go to the weight and not the admissibility of the opinion.[13] When the matter is beyond the witness's expertise, the trial court should not permit the witness to testify as an expert.[14] The trier-of-fact is entitled to consider an expert witness's opinion, but give it only the weight to which it deems the opinion is entitled.[15]

An expert may testify about behavioral characteristics of certain classes of persons, but the expert may not give an opinion about the accuracy, reliability, or truthfulness of a particular person, or quantify the percentage of such persons who are truthful.[16] Only when a defendant raises an insanity defense may an expert give an opinion of the defendant's state of mind at a given time.[17]

If the expert testimony is derived from application of a scientific principle or process, the party offering the evidence must show that the principle or process from which the testimony is derived has gained general acceptance in the particular field in which it belongs.[18] If the evidence is not derived from application of a scientific principle or process, but is instead the result of observing and identifying the way that certain things happen, there is no requirement that the party offering the evidence show general acceptance in the particular field in which it belongs.[19] When scientific evidence has been offered and received in other cases, if a party claims that the scientific principles in question have not gained general acceptance in the particular field, the party must introduce some authority to that effect before the trial court will require the other party to present evidence of general acceptance.[20]

Cases

702.010 To be admissible, expert testimony must (1) come from a qualified expert, (2) aid jurors in evaluating and understanding matters not within their common experience, (3) be reliable, and (4) have probative value not substantially outweighed by the danger of unfair prejudice.

State v. Lee(II),189 Ariz. 608, 944 P.2d 1222 (1997) (court concluded that detective's expert testimony on blood-spatter did not contradict opinion of medical examiner, thus rejected defendant's claim that detective's testimony was not reliable; because testimony helped jurors understand sequence of shots, and detective's non-inflammatory language was not unfairly prejudicial, testimony was admissible).

State v. Bolton,182 Ariz. 290, 896 P.2d 830 (1995) (because state did not provide sufficient showing that police officer's opinion about certain sex offenders wanting to restore dead victims to their original appearance was reliable, trial court erred in admitting this opinion, but any error was harmless).

State v. Velasco (Alday),165 Ariz. 480, 799 P.2d 821 (1990) (general acceptance in particular field in which it belongs does not mean universal or unanimous acceptance or that principle or process produces invariably accurate results, but instead means that principle or process is generally accepted as being capable of doing what it purports to do).

State v. Moran,151 Ariz. 378, 728 P.2d 248 (1986) (whether expert testimony will assist jurors' understanding of matter and balancing of probative value against prejudicial effect are generally fact-bound questions within competence of trial court; when admissibility of expert opinion evidence is question of "law or logic," it is responsibility of appellate court to determine admissibility).

Rourk v. State,170 Ariz. 6, 821 P.2d 273 (Ct. App. 1991) (because jurors undoubtedly knew that an intoxicated driver is far more likely to have an accident than a sober one, trial court did not abuse its discretion in excluding expert testimony that driver with a .147 percent BAC is 20 times more likely to be involved in an accident than a sober driver).

State ex rel. McDougall v. Riddel (Stahlbush),169 Ariz. 117, 817 P.2d 62 (Ct. App. 1991) (expert opinion on amount of alcohol in defendant's system, whether expressed as number of drinks or as BAC, provided jurors with relevant information).

State v. Richards,166 Ariz. 576, 804 P.2d 109 (Ct. App. 1990) (because witness was able to explain unique features of defendant's dental profile and how they compared to bite marks on victim, testimony was helpful to jurors).

702.020 To be admissible, expert testimony must (1) come from a qualified expert, (2) be an appropriate subject for expert testimony, (3) conform to a generally accepted scientific theory, and (4) have probative value not substantially outweighed by danger of unfair prejudice.

State v. Roscoe,184 Ariz. 484, 910 P.2d 635 (1996) (court held that expert opinion on eyewitness identification will not frequently meet standard for proper subject, and factors in determining admissibility are importance of eyewitness testimony and presence or absence of other evidence linking defendant to crime; because of extensive evidence linking defendant to crime and fact that case against defendant did not depend on eyewitness, trial court did not abuse discretion in precluding expert testimony on eyewitness identification).

State v. Velasco (Alday),165 Ariz. 480, 799 P.2d 821 (1990) (general acceptance in particular field in which it belongs does not mean universal or unanimous acceptance or that principle or process produces invariably accurate results, but instead means principle or process is generally accepted as being capable of doing what it purports to do).

State v. McCutcheon,162 Ariz. 54, 781 P.2d 31 (1989) (because no unusual factors surrounded eyewitness identification, and because testimony of expert would have been directed primarily at credibility of one witness, this was not appropriate for expert testimony).

702.030 Expert opinion testimony is admissible if it will assist the trier-of-fact to understand the evidence or to determine a fact in issue.

State v. Murray,184 Ariz. 9, 906 P.2d 542 (1995) (because shoe print comparisons are not ordinary and are beyond common experience, and because witness was qualified as expert and testimony about footprint comparisons would assist jurors to understand evidence, testimony was admissible, and any issues of proper methodology went to...