Persons who by reason of special study or experience possess special skill or knowledge in some science, art, profession, business or other activity not possessed by the average person are classified as “experts,” and testimony by them is referred to as “expert testimony.”5 Expert testimony is required when a claim requires proof of facts that are not within the common knowledge of laymen.5.1
Such testimony is usually offered through witnesses who have no direct knowledge of the facts, and their testimony is offered in the form of opinions based on facts otherwise in evidence and may also be based in whole or in part on facts perceived by or made known to the expert at or before the hearing. If the facts are not otherwise in evidence or even if the facts are not admissible in evidence, they may be relied upon by the expert if they are of a type reasonably relied upon by experts in a particular field in forming opinions or inferences on the subject.6 If the expert’s opinion is based in whole or in part upon the results of a test performed by or under the supervision of the expert, the expert must establish that the test is reasonably relied upon by experts in that field.7
If the court determines that the witness is qualified by knowledge, skill, experience or training to answer the questions propounded and that the scientific, technical or other specialized knowledge of the witness will assist the trier of fact to understand the evidence or to determine a fact in issue, the requirements for permitting expert opinion testimony will have been met.8 If a party challenges the qualifications of the expert, that objecting party is entitled to a hearing on voir dire. On voir dire the objecting party is entitled to cross-examine the proffered expert and, in appropriate cases, to present other evidence on the issue.9 The decision whether or not to admit expert testimony is within the discretion of the trial judge.9.1 In determining whether the expert testimony will be helpful to the jury, the court should consider (i) the jury’s knowledge presently existing about the subject of the proposed testimony, and (ii) the particular facts of the case.9.2
With respect to the scientific opinions of an expert, they will have to be shown to be based upon facts of a type reasonably relied upon by experts in the field in forming opinions or inferences on the subject matter of the proffered opinion.10 The proffered opinion will have to meet the standards applied to ordinary evidence.11 Chief among these are the requirements that the proffered opinions be relevant, that even if relevant their probative value not be substantially outweighed by the danger of unfair prejudice, confusion of the issues or misleading of the jury, and that the proffered opinions not occasion any delay, waste of time or needless presentation of cumulative evidence.12
Occasionally, a witness may be called who is a witness as to facts and is also an expert in a field relevant to his or her testimony. For example, an investigating police officer may testify as both a fact or witness expert. Similarly, a treating physician may testify in both capacities.12.1 To the extent the testimony is to facts only, the requirements for expert testimony do not have to be established, but the testimony offered by the witness must be on personal knowledge or on any other basis permitted by the Rules of Evidence for the admission of evidence of facts. If any inference or opinion as an expert is offered, the requirements for expert opinion must be established first. If the witness is called solely to testify as to facts, other requirements relating to expert witnesses, such as the requirement that all expert witnesses to be called be designated as such in the pre-trial order, will not apply to such witnesses.13
5. Condon v. State, 597 A.2d 7, 11 (Del. 1991), cert. denied, 128 L. Ed. 2d 53 (U.S. 1994); State v. Winsett, 205 A.2d 510, 521 (Del. Super. 1964); Board of Education v. 13 Acres of Land, 131 A.2d 180, 184 (Del. Super. 1957); Wilmington Housing Authority v. Harris, 93 A.2d 518, 522 (Del. Super. 1952); Culver v. Prudential Ins. Co., 179 A. 400 (Del. Super. 1935); Louft v. C. & J. Pyle Co., 75 A. 619, 622-23 (Del. Super. 1910); State v. Collins, 62 A. 224, 227 (Del. O. & T. 1903). See also D.R.E. 702.
5.1. Campbell v. DiSabatino, 947 A.2d 116, 1118 (Del. 2008); Davis v. Maute, 770 A.2d 36, 40 n.3 (Del. 2001).
6. D.R.E. 703.
7. Nelson v. State, 628 A.2d 69, 73 (Del. 1993); Santiago v. State, 510 A.2d 488, 489 (Del. 1986).
8. D.R.E. 702. See also South Atlantic S.S. Co. v. Munkacsy, 187 A. 600, 604 (Del. 1936), cert. denied, 299 U.S. 607 (1936).
9. See § 18:9.
9.1. Moorehead v. State, 538 A.2d 52, 56 (Del. 1994); State v. Magner, ID #9509007746, slip op. at 6, Alford, J. (Del. Super. Mar. 7, 1997).
9.2. State v. Magner, ID #9509007746, slip op. at 8-9, Alford, J. (Del. Super. Mar. 7, 1997).
10. D.R.E. 703; Nelson v. State, 628 A.2d 69, 73-74(Del. 1993); Santiago v. State, 510 A.2d 488, 489 (Del. 1986).
11. Nelson v. State, 628 A.2d 69, 73-74 (Del. 1993).
12. D.R.E. 401, 402, 403.
12.1. S. Muoio & Co. LLC v. Hallmark Entm’t nvs. Co., C.A. No. 4729-CC, slip op. at 3 & n.4, Chandler, C. (Del. Ch. Sept. 16, 2010).
13. Duphily v. Delaware Elec. Coop., 662 A.2d 821, 835-36 (Del. 1995); McLain v. General Motors Corp., 569 A.2d 579, 584 (Del. 1990). See also State v. Adams, Cr. A. No. N85-10-0l 16T, slip op. at 5-6, Gebelein, J. (Del. Super. Nov. 4, 1987), reprinted in Hamann v. State, 565 A.2d 924, 930 (Del. 1989) (criminal defendant could call State’s expert for the limited purpose of explaining a testing process).
© 2010 David L. Finger