Guide to Evidence  Section 705. Disclosure of facts or data underlying expert opinion

Unless the court orders otherwise, an expert may state an opinion—and give the reasons for it—without first testifying to the underlying facts or data. But the expert may be required to disclose those facts or data on cross-examination. However, in criminal cases, an expert for the Commonwealth may not offer an opinion that depends on underlying facts or data that are testimonial hearsay.

This section is largely taken from Proposed Mass. R. Evid. 705, which the Supreme Judicial Court adopted in Department of Youth Servs. v. A Juvenile, 398 Mass. 516, 532 (1986).

“The rule is aimed principally at the abuse of the hypothetical question. It does not eliminate the availability of the hypothetical question, but only the requirement of its use. . . . The thrust of the rule is to leave inquiry regarding the basis of expert testimony to cross-examination, which is considered an adequate safeguard.”

Id., quoting Advisory Committee’s Note on Proposed Mass. R. Evid. 705. Under Massachusetts law, for purposes of direct examination, there is a “distinction between an expert’s opinion on the one hand and the hearsay information that formed the basis of the opinion on the other, holding the former admissible and the latter inadmissible.” Commonwealth v. Greineder, 464 Mass. 580, 584, cert. denied, 571 U.S. 865 (2013). However, after Commonwealth v. Gordon, 496 Mass. 554, 575 (2025), a Commonwealth's expert in a criminal case may not offer an opinion that depends on facts or data that constitute testimonial hearsay.

On cross-‌examination, as a matter of trial strategy, the opposing party may choose to elicit the hearsay basis for an opinion offered on direct examination. See Commonwealth v. Chism, 495 Mass. 358, 379 (2025); Commonwealth v. Nardi, 452 Mass. 379, 387–395 (2008). In Commonwealth v. Barbosa, 457 Mass. 773, 785–787 (2010), cert. denied, 563 U.S. 990 (2011), the Supreme Judicial Court stated the direct examination of an expert on facts not in evidence

“is limited to the expert’s opinion and matters of which the expert had personal knowledge, such as her training and experience, and the protocols generally accepted in her field of expertise. Only the defendant can open the door on cross-‌examination to testimony regarding the basis for the expert’s opinion, which may invite the expert witness to testify to facts or data that may be admissible in evidence but have not yet been admitted in evidence.”

Accord Commonwealth v. Leng, 463 Mass. 779, 783–785 (2012); Nardi, 452 Mass. at 387-395. “If the door is opened by the opposing party, on redirect examination, the proponent of the evidence then may introduce additional details surrounding the source of the expert’s opinion.” Chism, 495 Mass. at 379.

Cross-Reference: Section 703, Bases of Opinion Testimony by Experts; Introductory Note to Article VIII, Hearsay.

Limitation on cross-examination

Under certain circumstances, the requirement that the expert disclose underlying facts or data on cross-‌examination may be limited by Section 403 considerations. See Commonwealth v. Anestal, 463 Mass. 655, 668–669 (2012). In Anestal, the court held that

“[o]nce the Commonwealth sought to inquire over objection about this prior bad act evidence, it was incumbent on the judge in the sound exercise of his discretion to ascertain whether the evidence was probative and, if so, whether that probative value was substantially outweighed by the danger of unfair prejudice to the defendant.”

Id. at 669. This inquiry should take place at sidebar, or the judge should conduct a voir dire. Id. at 669 n.20.