Delaware Trial Handbook § 18:8. FACTUAL BASIS OF EXPERT OPINION

Prior to 2001, D.R.E. 705(a) required that, before an expert could render an opinion, the expert had to first identify the facts and data upon which the opinion was based and give the reasons for the opinion.92 In 2001, the rule was changed to remove that requirement. The change tracks Federal Rule of Evidence 705. According to the Federal Advisory Committee Notes, the change was made in recognition of the fact that the underlying data can be obtained in pre-trial discovery, and that any weaknesses in the expert’s opinion can be brought out in cross-examination.93

Further protection appears in D.R.E. Section 705(b), which provides that an adverse party may object to the testimony of an expert on the ground that the expert does not have a sufficient basis for the opinion. The trial court has discretion to allow the adverse party, before the expert gives an opinion, to conduct a voir dire examination directed and limited to the underlying facts or data upon which the opinion is based.94 Such voir dire to be conducted in the presence of or outside the presence of the jury.95

The facts or data in a particular case upon which an expert bases an opinion or inference may be those perceived by or made known to the expert at or before the hearing. The facts or data upon which an expert opinion is based may include inadmissible data that experts in the field would reasonably rely upon in reaching their conclusions.97 This rule frees experts to use sources that they would normally use outside of court and so avoids the time and expense involved in producing various authenticating witnesses.97 Thus, when a qualified expert testifies based upon a test, the expert need only show that the test is reasonably relied upon by experts in the field.98 If an expert relies upon documents as the basis for an opinion, the fact that the expert cannot recall at trial the specific contents of the documents will not render the witness’s testimony inadmissible.99 When the expert relies on the oral representation of another person to reach a conclusion, however, the jury must determine the credibility of both the expert and the expert’s source of information.100

The rule permitting an expert to testify based on inadmissible evidence does not necessarily permit a party to bring in evidence that had previously been ruled inadmissible merely by having an expert rely on that evidence.101 Further, legally incorrect assumptions are not facts upon which experts are entitled to rely in forming their opinions.102

In the discretion of the trial judge, the opinion of an expert may, but need not, be adduced through the use of hypothetical questions.103 This was the general practice prior to the adoption of the Delaware Rules of Evidence and was mandated where the expert did not have knowledge of the facts through direct observation. Where hypothetical questions are used, they must be based upon facts in evidence and/or recognized empirical data.104

92. Former D.R.E. 705(a). See also Fensterer v. State, 509 A.2d 1106, 1109 (Del. 1986); Eaton v. State, 394 A.2d 217, 219 (Del. 1978); Bates v. State, 386 A.2d 1139, 1144 (Del. 1978); Hercules Powder Co. v. Di Sabatino, 188 A.2d 529, 533 (Del. 1963), overruled on other grounds by Delmarva Power & Light Co. v. Burrows, 435 A.2d 716 (Del. 1981) as stated in Sirmans v. Penn, 588 A.2d 1103 (Del. 1991) (common law rule); Cebenka v. Upjohn Co., C.A. No. 80C-AP-76, slip op. at 2, Gebelein, J. (Del. Super. May 27, 1988).

93. F.R.E. 705, Advisory Committee Note.

94. D.R.E. 705(b); Re v. State, 540 A.2d 423, 426 (Del. 1988).

95. D.R.E. 104(c).

96. D.R.E. 703; Stewart v. Dept. of Services for Children, Youth and Their Families, 991 A.2d 750, 757-58 (Del. 2010); McCloskey v. State, 457 A.2d 332, 336 (Del. 1983); Lynch v. Athey Products Corp., 505 A.2d 42, 44 (Del. Super. 1985).

97. Ramada Inns, Inc. v. Dow Jones & Co., C.A. No. 83C-AU-56, slip op. at 14, Poppiti, J. (Del. Super. Mar. 10, 1988).

98. State v. Pennell, 584 A.2d 513, 515 (Del. Super. 1989); Santiago v. State, 510 A.2d 488, 489-90 (Del. 1986); State v. Nelson, Cr. A. Nos. 1K89-09-0882-0884, slip op. at 3, Gebelelein, J. (Del. Super. Sept. 11, 1991, revised, Oct. 17, 1991), app. denied mem., 609 A.2d 730 (Del. 1991). This rule has no bearing if the expert’s opinion is based solely on his or her own experience. Pennell v. State, 602 A.2d 48, 55 (Del. 1991).

99. DiSabatino v. Liddicoat, No. 464, 1988, slip op. at 11, Horsey, J. (Del. Aug. 30, 1990) (ORDER), disposition reported at 582 A.2d 934 (Del. 1990) (TABLE).

100. Alabama By-Products Corp. v. Neal, 588 A.2d 255, 258 (Del. 1991); Re v. State, 540 A.2d 423, 427 (Del. 1988).

101. Ramada Inns v. Dow Jones & Co., C.A. No. 83C-AU-56, slip op. at 15-16, Poppiti, J. (Del. Super. Mar. 10, 1988). Compare Farrall v. A. C. & S. Co., C.A. No. 85C.FE-10, slip op. at 1-2, Taylor, J. (Del. Super. June 12, 1989) (permitting expert to rely on facts and data held inadmissible as not being authenticated in separate trial).

102. Wilmington v. Parcel of Land, 607 A.2d 1163, 1170 (Del. 1992).

103. Storey v. Castner, 314 A.2d 187, 192 (Del. 1973). See also D.R.E. 705, comment.

104. Sears, Roebuck & Co. v. Facciolo, 320 A.2d 347, 350 (Del. 1974).

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