Rule 705. Disclosing the Facts or Data Underlying an Expert’s Opinion.

 If an expert states an opinion the expert must state the facts or data on which the opinion is based.

   The text and substance of Pa.R.E. 705 differ significantly from F.R.E. 705. The Federal Rule generally does not require an expert witness to disclose the facts upon which an opinion is based prior to expressing the opinion. Instead, the cross-examiner bears the burden of probing the basis of the opinion. Pennsylvania does not follow the Federal Rule. See Kozak v. Struth, 515 Pa. 554, 560, 531 A.2d 420, 423 (1987) (declining to adopt F.R.E. 705, the Court reasoned that ‘‘requiring the proponent of an expert opinion to clarify for the jury the assumptions upon which the opinion is based avoids planting in the juror’s mind a general statement likely to remain with him in the jury room when the disputed details are lost.’’) Relying on cross-examination to illuminate the underlying assumption, as F.R.E. 705 does, may further confuse jurors already struggling to follow complex testimony. Id.

   Accordingly, Kozak requires disclosure of the facts used by the expert in forming an opinion. The disclosure can be accomplished in several ways. One way is to ask the expert to assume the truth of testimony the expert has heard or read. Kroeger Co. v. W.C.A.B., 101 Pa. Cmwlth. 629, 516 A.2d 1335 (1986); Tobash v. Jones, 419 Pa. 205, 213 A.2d 588 (1965). Another option is to pose a hypothetical question to the expert. Dietrich v. J.I. Case Co., 390 Pa. Super. 475, 568 A.2d 1272 (1990); Hussey v. May Department Stores, Inc., 238 Pa. Super. 431, 357 A.2d 635 (1976).

   When an expert testifies about the underlying facts and data that support the expert’s opinion and the evidence would be otherwise inadmissible, the trial judge upon request must, or on the judge’s own initiative may, instruct the jury to consider the facts and data only to explain the basis for the expert’s opinion, and not as substantive evidence.

   Official Note

   Adopted May 8, 1998, effective October 1, 1998; rescinded and replaced January 17, 2013, effective March 18, 2013.

   Committee Explanatory Reports:

   Final Report explaining the January 17, 2013 rescission and replacement published with the Court’s Order at 43 Pa.B. 651 (February 2, 2013).

   The provisions of this Rule 705 rescinded and replaced January 17, 2013, effective in sixty days, 43 Pa.B. 620. Immediately preceding text appears at serial page (299644).