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Guide to Evidence

Guide to Evidence Article VII: Opinion and expert evidence

Adopted Date: 01/01/2021


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Table of Contents

Section 701. Opinion testimony by lay witnesses

If a witness is not testifying as an expert, testimony in the form of an opinion is limited to one that is 

(a) rationally based on the witness’s perception; 

(b) helpful to a clear understanding of the witness’s testimony or in determining a fact in issue; and 

(c) not based on scientific, technical, or other specialized knowledge within the scope of Section 702.


This section, which is taken nearly verbatim from Fed. R. Evid. 701, reflects Massachusetts practice. See Noyes v. Noyes, 224 Mass. 125, 129 (1916); Commonwealth v. Sturtivant , 117 Mass. 122, 133, 137 (1875); Commonwealth v. Brusgulis, 41 Mass. App. Ct. 386, 390–391 (1996). “While an expert opinion is admissible only where it will help jurors interpret evidence that lies outside of common experience, a lay opinion is admissible only where it lies within the realm of common experience” (quotation omitted). Commonwealth v. Canty, 466 Mass. 535, 541–542 (2013) . Where the same witness gives both lay and expert testimony, the better practice is for the trial judge to instruct the jury about the difference. Commonwealth v. Mason, 485 Mass. 520, 531–532 (2020). “The rule that witnesses in describing conduct should tell what they saw and heard does not foreclose the use of words of summary description.” Kane v. Fields Corner Grille, Inc., 341 Mass. 640, 647 (1961) (judge had the discretion to permit witnesses to use the words “boisterous” and “in an arrogant manner” in describing the actions of a person they observed). Accord Commonwealth v. Bonomi, 335 Mass. 327, 339 (1957) (condition of nervousness or happiness); Commonwealth v. Fuller , 66 Mass. App. Ct. 84, 91 (2006). See also Commonwealth v. Bonds , 445 Mass. 821, 830 (2006); McGrath v. Fash , 244 Mass. 327, 329 (1923) (witness permitted to testify that “all of a sudden this truck came around the corner on two wheels, and zigzagging across the street and appeared to be out of the control of the driver”); Commonwealth v. Rodziewicz, 213 Mass. 68, 69 (1912) (it was error to permit a police investigator to identify points of origin of a fire based simply on observations about condition of the burned structure). 

Ultimately, the admission of summary descriptions of observed facts is left to the discretion of the trial judge. Kane v. Fields Corner Grille, Inc., 341 Mass. at 647 (“Trials are not to be delayed and witnesses made inarticulate by too nice objections or rulings as to the use of such descriptive words.”). See Com­monwealth v. Barbosa, 477 Mass. 658, 673–674 (2017) (witness may testify about time discrepancy between video surveillance footage and GPS data to explain “investigative significance” of evidence). A witness may not express an opinion about the credibility of another witness. See Commonwealth v. Triplett , 398 Mass. 561, 567 (1986). 

Illustrations. When due to the complexity of expressing the observation such evidence might otherwise not be available, witnesses are permitted, out of necessity, to use “shorthand expressions” to describe observed facts such as the identity, size, distance, and speed of objects; the length of the passage of time; and the age, identity, and conduct of persons. See Commonwealth v. Tracy , 349 Mass. 87, 95–96 (1965); Noyes v. Noyes , 224 Mass. 125, 129–130 (1916); Ross v. John Hancock Mut. Life Ins. Co. , 222 Mass. 560, 562 (1916). 

Cellular Phone Positioning. A lay witness is not permitted to testify to the intra-cell site position of a phone user because the testimony requires specialized knowledge that relates to the scientific and technological features of cell sites. Commonwealth v. Gonzalez , 475 Mass. 396, 412 n.37 (2016).

Identity. The general rule is that a witness’s opinion concerning the identity of a person depicted in a photograph or video is admissible where that witness is more likely to correctly identify the person from the photo or video than is the jury. Commonwealth v. Pina, 481 Mass. 413, 429–430 (2019).  Compare Commonwealth v. Vitello , 376 Mass. 426, 459–460 & n.29 (1978) (allowing police officer to testify that a photograph selected by a witness depicted the defendant because his appearance had changed since the date of the offense), and Commonwealth v. Pleas , 49 Mass. App. Ct. 321, 323–329 (2000) (allowing police officer to testify that man depicted in a surveillance videotape who was holding the victim was the defendant “because [1] the image in the videotape and the prints made from it were of poor quality . . . ; [2] [the officer] had long familiarity with the defendant that enabled him to identify an indistinct picture of the defendant; [3] there was some change in the appearance of the defendant at trial and as he generally presented in everyday life outdoors; and [4] the acquaintanceship of [the officer] with the defendant, as it was presented to the jury, was social rather than tied to [the officer’s] duties as a police officer”), with Commonwealth v. Wardsworth, 482 Mass. 454, 476 (2019) (reversible error to allow police officer to identify person in a surveillance videotape as the defendant because the jury was equally capable of making the determination),  and Commonwealth v. Nassar , 351 Mass. 37, 41–42 (1966) (because a sketch and a photograph of the defendant were in evidence, the jury did not require any assistance from a witness who was asked whether they were a likeness of the defendant). See also Commonwealth v. Connolly, 91 Mass. App. Ct. 580, 591–593 (2017) (police officer’s testimony that person in surveillance video that was inadvertently erased was the defendant was not helpful to jury without foundation providing “enough information to allow the jury to conduct an independent assessment of the accuracy and reliability of his identifications”; rejecting cat­egorical approach to exclusion of such evidence).

Intent. This section does not permit a witness to express an opinion about what someone was intending or planning to do based on an observation of the person. See Commonwealth v. Jones , 319 Mass. 228, 230 (1946). A lay witness may not express an opinion about what another person was intending or planning to do based on observations of that person’s conduct. Borella v. Renfro, 96 Mass. App. Ct. 617, 625 n.22 (2019).

Internet Searches. A lay witness may describe an Internet search and its results, as the search does not require specialized knowledge. Commonwealth v. Mason, 485 Mass. 520, 538–539 (2020).

Mental Capacity. A lay opinion as to sanity or mental capacity is permitted only by an attesting witness to a will and only as to the testator’s mental condition at the time of its execution. See Holbrook v. Seagrave , 228 Mass. 26, 29 (1917); Commonwealth v. Spencer , 212 Mass. 438, 447 (1912). “Although a lay witness may not testify about whether another person suffered from mental illness, such a witness is permitted to ‘testify to facts observed.’” Commonwealth v. Sliech-Brodeur , 457 Mass. 300, 330 n.43 (2010), quoting Commonwealth v. Monico , 396 Mass. 793, 803 (1986). See Commonwealth v. Dobbins, 96 Mass. App. Ct. 593, 597–598 (2019) (testimony of victim’s grandmother that victim had learning disability not improper lay opinion).


  • AlcoholA police officer or lay witness may provide an opinion, in summary form, about another person’s sobriety, provided there exists a basis for that opinion. Commonwealth v. Orben , 53 Mass. App. Ct. 700, 704 (2002). Where a defendant is charged with operating a vehicle while under the influence of alcohol, a police officer who observed the defendant may offer an opinion as to the defendant’s level of intoxication but may not offer an opinion as to whether the defendant’s intoxication impaired his ability to operate a motor vehicle, because the latter comes too close to an opinion on the defendant’s guilt. Commonwealth v. Canty , 466 Mass. 535, 545 (2013). As a lay witness, a police officer may testify to the administration and results of field sobriety tests that measure a person’s balance, coordination, and acuity of mind in understanding and performing simple instructions, as a juror understands from common experience and knowledge that “intoxication leads to diminished balance, coordination, and mental acuity.” Commonwealth v. Sands , 424 Mass. 184, 187 (1997) (contrasting the Horizontal Gaze Nystagmus Test, which requires expert testimony, from “ordinary” field sobriety tests such as a nine-step walk and turn and recitation of the alphabet); Id. at 186 (“Expert testimony on the scientific theory is needed if the subject of expert testimony is beyond the common knowledge or understanding of the lay juror.”). 
  • Marijuana. Where a defendant is charged with operating a motor vehicle under the influence of marijuana, a police officer may testify as a lay witness as to his or her observations of the defendant’s performance of the one-leg stand test and the nine-step walk-‌and-‌turn test. Commonwealth v. Gerhardt, 477 Mass. 775, 783 (2017). These observations are admissible to the extent that they are pro­bative of “a defendant’s balance, coordination, ability to retain and follow directions, and ability to perform tasks requiring divided attention,” as well as “the presence or absence of other skills necessary for the safe operation of a motor vehicle.” Id. However, a police officer may not testify that a defendant charged with operating under the influence of marijuana “passed” or “failed” a field sobriety test. Id. at 784. Lay witnesses and police officers also may not present testimony indicating that, in their opinion, a defendant was under the influence of marijuana. Id. A testifying witness “should” refer to field sobriety tests as “roadside assessments.” Id. at 785. A trooper’s testimony limited to what he or she asked the defendant to do and his or her observations of what the defendant did is permissible descriptive testimony, not impermissible evaluative testimony. Commonwealth v. Smith, 95 Mass. App. Ct. 437, 443–444 (2019).

Cross-Reference: Note “Effect of Intoxicants” to Section 702, Testimony by Expert Witnesses.

Sounds. In  Commonwealth v. Sturtivant , 117 Mass. 122, 133 (1875), the Supreme Judicial Court stated that a witness “may state his opinion in regard to sounds, their character, from what they proceed, and the direction from which they seem to come.” 

Struggle. An experienced police officer, or possibly even a lay witness, could opine on whether a scene was suggestive of a struggle. Commonwealth v. Burgess , 450 Mass. 422, 436 n.8 (2008).

Value. Depending on the circumstances, opinion testimony about the value of real or personal property may be given by lay witnesses or expert witnesses. With regard to lay witnesses, 

“[t]he rule which permits the owner of real or personal property to testify as to its value does not rest upon the fact that he holds the legal title. The mere holding of the title to property by one who knows nothing about it and perhaps has never even seen it does not rationally and logically give him any qualification to express an opinion as to its value. Ordinarily an owner of property is actually familiar with its characteristics, has some acquaintance with its uses actual and potential and has had experience in dealing with it. It is this familiarity, knowledge and experience, not the holding of the title, which qualify him to testify as to its value.” 

Menici v. Orton Crane & Shovel Co., 285 Mass. 499, 503 (1934). An owner of a small business may give an opinion about the company’s value where the owner is fully aware of the contracts that the business has and its liabilities. Spinosa v. Tufts, 98 Mass. App. Ct. 1, 11 (2020). This same principle applies to a landowner’s opinion as to the value of property. von Henneberg v. Generazio, 403 Mass. 519, 524 (1988). A lay witness also may testify to the value of his or her own services. Berish v. Bornstein, 437 Mass. 252, 273 (2002). But see Turner v. Leonard, Inc., 17 Mass. App. Ct. 909, 910–911 (1983) (owner was not so familiar with his automobile to permit him to offer an opinion as to its value).

Section 702. Testimony by expert witnesses

See also: Supplement to the 2021 Guide to Evidence

A witness who is qualified as an expert by knowledge, skill, experience, training, or education may testify in the form of an opinion or otherwise if 

(a) the expert’s scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue; 

(b) the testimony is based on sufficient facts or data; 

(c) the testimony is the product of reliable principles and methods; and 

(d) the expert has reliably applied the principles and methods to the facts of the case.


Introduction. This section, which is based upon Fed. R. Evid. 702 and Proposed Mass. R. Evid. 702, reflects Massachusetts law. There are two methods by which the judge may satisfy his or her duty as the gatekeeper to ensure that expert witness testimony is reliable: (1) the “Frye” test, i.e., general acceptance in the relevant scientific community, or (2) a Daubert-Lanigan analysis. Commonwealth v. Powell , 450 Mass. 229, 238 (2007). See Daubert v. Merrell Dow Pharms., Inc. , 509 U.S. 579, 585–595 (1993), and Commonwealth v. Lanigan , 419 Mass. 15, 24–26 (1994). 

It is important to distinguish between the words used to express the principle of Massachusetts law set forth in this section and the application of the principle in specific cases. As the following notes indicate, the framework used under the Federal rules and in Massachusetts is the same, and each approach is specifically described as flexible. The principal difference is that in Massachusetts, the trial judge satisfies his or her gatekeeper responsibilities under Subsections (b) and (c) once the proponent of the evidence establishes that it is generally accepted by the relevant scientific community. See Commonwealth v. Patterson , 445 Mass. 626, 640–641 (2005); Commonwealth v. Sands , 424 Mass. 184, 185–186 (1997). Compare Commonwealth v. Lanigan, 419 Mass. at 26 (“We accept the basic reasoning of the Daubert opinion because it is consistent with our test of demonstrated reliability. We suspect that general acceptance in the relevant scientific community will continue to be the significant, and often the only, issue.”), and Canavan’s Case , 432 Mass. 304, 314 n.5 (2000) (“Application of the Lanigan test requires flexibility. Differing types of methodology may require judges to apply differing evaluative criteria to determine whether scientific methodology is reliable. In the Lanigan case, we established various guideposts for determining admissibility including general acceptance, peer review, and testing.”), with Daubert v. Merrell Dow Pharms., Inc., 509 U.S. at 594–595 (“The inquiry envisioned by [Fed. R. Evid.] 702 is, we emphasize, a flexible one. Its overarching subject is the scientific validity—and thus the evidentiary relevance and reliability—of the principles that underlie a proposed submission.”), and Kumho Tire Co. v. Carmichael , 526 U.S. 137, 141 (1999) (“[T]he test of reliability is ‘flexible,’ and Daubert’s list of specific factors neither necessarily nor exclusively applies to all experts or in every case.”). See also Kumho Tire Co. v. Carmichael, 526 U.S. at 150 (“Daubert makes clear that the factors it mentions do not constitute a ‘definitive checklist or test.’ [Daubert v. Merrell Dow Pharms., Inc., 509 U.S.] at 593. And Daubert adds that the gatekeeping inquiry must be ‘tied to the facts’ of a particular ‘case.’ Id. at 591.” [Quotation and citation omitted.]); Daubert v. Merrell Dow Pharms., Inc., 509 U.S. at 594 (“Widespread acceptance can be an important factor in ruling particular evidence admissible, and a known technique which has been able to attract only minimal support within the community[] may properly be viewed with skepticism” [quotation and citation omitted].). 

Hearing. An evidentiary hearing is not always necessary to comply with  Commonwealth v. Lanigan ,  419 Mass. 15 (1994). See Palandjian v. Foster , 446 Mass. 100, 111 (2006); Vassallo v. Baxter Healthcare Corp. , 428 Mass. 1, 1–13 (1998) (trial judge properly relied on affidavits and transcripts of testimony from other cases). However, as the Supreme Judicial Court noted, “we have not ‘grandfathered’ any particular theories or methods for all time, especially in areas where knowledge is evolving and new understandings may be expected as more studies and tests are conducted.” Commonwealth v. Shanley , 455 Mass. 752, 763 n.15 (2010) (court acknowledged it was prudent for trial judge to conduct an evidentiary hearing in connection with expert testimony about dissociative amnesia because of “the evolving nature of scientific and clinical studies of the brain and memory”); Commonwealth v. Camblin , 471 Mass. 639, 648 (2015) (fact that the Legislature may prescribe rules of evidence and methods of proof employed in trials “does not mean that the reliability of every type of evidence the Legislature may deem admissible, particularly in a criminal case, is automatically insulated from challenge and review on reliability grounds”). If a defendant does not file a pretrial motion requesting a Daubert-Lanigan hearing to challenge the general scientific reliability of the methodology, the issue is waived on appeal. Commonwealth v. Wilkerson, 486 Mass. 159, 172 (2020). A trial judge’s decision on whether expert witness evidence meets the Lanigan standard of reliability is reviewed on appeal under an abuse of discretion standard. See General Elec. Co. v. Joiner , 522 U.S. 136, 141–143 (1997); Canavan’s Case , 432 Mass. 304, 311–312 (2000). 

Five Foundation Requirements. The proponent of expert witness testimony has the burden of establishing the five foundation requirements for the admission of such testimony under this section. See Commonwealth v. Barbosa , 457 Mass. 773, 783 (2010) (explaining the five foundation requirements). First, the proponent must establish that the expert witness testimony will assist the trier of fact. See Commonwealth v. Francis , 390 Mass. 89, 98 (1983); Commonwealth v. Rodziewicz , 213 Mass. 68, 69–70 (1912). Second, the proponent must demonstrate that the witness is qualified as an expert in the relevant area of inquiry. See Commonwealth v. Frangipane , 433 Mass. 527, 535–536 (2001); Commonwealth v. Boyd , 367 Mass. 169, 182 (1975). Third, the proponent must demonstrate that the facts or data in the record are sufficient to enable the witness to give an opinion that is not merely speculation. See Lightlab Imaging, Inc. v. Axsun Techs., Inc. , 469 Mass. 181, 191 (2014). Fourth, the expert opinion must be based on a body of knowledge, a principle, or a method that is reliable.  Commonwealth v. Lanigan ,  419 Mass. 15, 26 (1994). Fifth, the proponent must demonstrate that the expert has applied the body of knowledge, the principle, or the method in a reliable manner to the particular facts of the case. See Commonwealth v. Patterson , 445 Mass. 626, 645–648 (2005); Commonwealth v. McNickles , 434 Mass. 839, 850 (2001). 

Each of these five foundation requirements is a preliminary question of fact for the trial judge to determine under Section 104(a), Preliminary Questions: In General. The trial judge has “broad discretion” in making these determinations. Commonwealth v. Robinson , 449 Mass. 1, 5 (2007). In making these preliminary determinations, the trial judge may be required to resolve disputes as to the credibility of witnesses. Commonwealth v. Patterson, 445 Mass. at 647–648. Expert witness testimony should not be deemed unreliable simply because there is a disagreement of opinion or in terms of the level of confidence among the experts. See Commonwealth v. Torres , 442 Mass. 554, 581 (2004). 

The judge has no authority to exclude the evidence because he or she disagrees with the expert’s opinion or finds the testimony unpersuasive. See Commonwealth v. Roberio , 428 Mass. 278, 281 (1998) (“Once the expert’s qualifications were established and assuming the expert’s testimony met the standard of  Commonwealth v. Lanigan ,  419 Mass. 15 [1994], the issue of credibility was for a jury, not the judge.”). When an expert’s opinion is based on the analysis of complex facts, the failure of the expert to account for all the variables goes to its weight and not its admissibility. Salvas v. Wal-Mart Stores, Inc. , 452 Mass. 337, 359–360 (2008). See id. at 351–360 (expert witness with doctorate in psychology and mathematics used statistical methods to evaluate large body of employee records to account for missing records and to opine that employer had wrongfully deprived employees of compensation). 

First Foundation Requirement: Assistance to the Trier of Fact. “The role of an expert witness is to help jurors interpret evidence that lies outside of common experience.” Commonwealth v. Tanner , 45 Mass. App. Ct. 576, 581 (1998). Thus, expert testimony may be excluded when it will not assist the jury. See Commonwealth v. Tolan , 453 Mass. 634, 648 (2009) (trial judge has discretion “to preclude expert testimony on commonly understood interrogation methods”); Commonwealth v. Bly , 448 Mass. 473, 496 (2007) (trial judge did not abuse his discretion in excluding expert witness testimony on the subject of cross-racial identification). Expert witness testimony also may be excluded because it is cumulative. See Anthony’s Pier Four, Inc. v. HBC Assocs. , 411 Mass. 451, 482 (1991). Expert witness testimony may be excluded because it does not fit the facts of the case. See Ready, petitioner , 63 Mass. App. Ct. 171, 179 (2005) (concluding that a diagnostic test known as the Abel Assessment of Sexual Interest [AASI] was of no value to the fact issues facing the jury). See generally Section 403, Excluding Relevant Evidence for Prejudice, Confusion, Waste of Time, or Other Reason. Finally, expert witness testimony may be excluded as not probative of a material fact in dispute and thus of no assistance to the jury when it amounts to a mere guess or conjecture. See Kennedy v. U-Haul Co. , 360 Mass. 71, 73–74 (1971). See also Section 402, General Admissibility of Relevant Evidence. There are circumstances, however, in which an expert witness’s opinion as to a possibility will have probative value. See Commonwealth v. Federico , 425 Mass. 844, 852 (1997). The trial judge has discretion to determine whether expert witness testimony will assist the trier of fact. See, e.g., Commonwealth v. Francis , 390 Mass. 89, 95–102 (1983) (expert witness testimony on the reliability of eyewitness identification evidence); Commonwealth v. Trainor , 374 Mass. 796, 801 (1978) (“A properly conducted public opinion survey, offered through an expert in conducting such surveys, is admissible in an obscenity case if it tends to show relevant standards in the Commonwealth.”).

Second Foundation Requirement: Qualifications of the Expert. “The crucial issue in determining whether a witness is qualified to give an expert opinion is whether the witness has sufficient education, training, experience and familiarity with the subject matter of the testimony” (quotations and citation omitted). Commonwealth v. Richardson, 423 Mass. 180, 183 (1996). See Adoption of Hugo, 428 Mass. 219, 232–234 (1998) (license clinical social worker); Custody of Michel, 28 Mass. App. Ct. 260, 266 (1990) (investigator appointed under G. L. c. 119, § 24). Qualification of a witness as an expert in accordance with Section 104(a), Preliminary Questions: In General, does not always require an explicit ruling on the record by the judge. However, if a formal ruling is made, it should be made outside the hearing of the jury. Id. at 184. 

“Whether an expert determined to be qualified in one subject is also qualified to testify in another, related subject will depend on the circumstances of each case, and, where an expert has been determined to be qualified, questions or criticisms as to whether the basis of the expert’s opinion is reliable go to the weight, and not the admissibility, of the testimony.” 

Commonwealth v. Crouse , 447 Mass. 558, 569 (2006) (noting that there must always be a first time for every expert witness). However, the trial judge, acting as the gatekeeper, must enforce boundaries between areas of expertise within which the expert is qualified and areas that require different training, education, and experience and within which the expert is not qualified. See Commonwealth v. Frangipane , 433 Mass. 527, 535 (2001) (social worker qualified to testify as an expert witness that abused children may experience dissociative memory loss and recovered memory, but was not qualified to testify about how trauma victims store and retrieve or dissociate memories); Commonwealth v. Bouley, 93 Mass. App. Ct. 709, 714–715 (2018) (EMT qualified to opine that defendant had overdosed on opioids).

Third Foundation Requirement: Knowledge of Sufficient Facts or Data in the Record. The basis of expert opinion may include the factors set forth in Section 703, namely: (a) facts observed by the witness or otherwise in the witness’s direct personal knowledge; (b) evidence already in the record or which the parties represent will be presented during the course of the proceedings, which facts may be assumed to be true in questions put to the witness; and (c) facts or data not in evidence if the facts or data are independently admissible in evidence and are a permissible basis for an expert to consider in formulating an opinion. See Section 703, Bases of Opinion Testimony by ExpertsLaClair v. Silberline Mfg. Co., 379 Mass. 21, 32 (1979). See also Department of Youth Servs. v. A Juvenile , 398 Mass. 516, 531 (1986). This requirement means the expert witness 

“must have sufficient familiarity with the particular facts to reach a meaningful expert opinion. The relevant distinction is between an opinion based upon speculation and one adequately grounded in facts. Although a trial judge has some discretion in making that distinction, it may be an abuse of discretion to disallow expert testimony which is based upon reasonably adequate familiarity with the facts.” (Citations omitted.) 

Fourth St. Pub, Inc. v. National Union Fire Ins. Co., 28 Mass. App. Ct. 157, 161 (1989). Contrast Commonwealth v. Talbot, 444 Mass. 586, 589 (2005) (no error in excluding defense expert who was proffered to testify about the effects of hypoglycemic shock in view of the absence of any evidence that the defendant experienced such a condition at the time of the offense); Commonwealth v. Laliberty, 373 Mass. 238, 241 (1977) (opinion concerning defense of lack of criminal responsibility not admissible absent evidence that defendant suffered from mental disease or defect at time of crime). Questions posed to a witness on cross-examination may qualify the witness to offer expert testimony on redirect examination. Motsis v. Ming’s Supermarket, Inc., 96 Mass. App. Ct. 371, 381–382 (2019).

Fourth Foundation Requirement: Reliability of Principle or Method Used by the Expert. Both the United States Supreme Court, applying Fed. R. Evid. 702 in Daubert v. Merrell Dow Pharms., Inc., 509 U.S. 579 (1993), and the Supreme Judicial Court applying the common law in  Commonwealth v. Lanigan,  419 Mass. 15 (1994), agree on the fundamental requirement that “[i]f the process or theory underlying [an] . . . expert’s opinion lacks reliability, that opinion should not reach the trier of fact.” Commonwealth v. Lanigan, 419 Mass. at 26. A conclusory statement that an expert is “trained” in a particular field is insufficient to establish the reliability of the methodology in which the expert claims to be trained. See Commonwealth v. Franceschi, 94 Mass. App. Ct. 602, 609–610 (2018) (accident reconstruction expert should not have been permitted to testify that mark on road was “scuff mark” left by shoe where testimony simply stated his conclusion based on his training and experience and did not explain methodology by which conclusion was reached). Both the Supreme Court and the Supreme Judicial Court require the trial judge to act as a gatekeeper to ensure that the expert witness testimony that is considered by the jury meets minimum standards of reliability. The variation between the two approaches is that Massachusetts law makes general acceptance the default position and a Daubert analysis an alternative method of establishing reliability. Under Fed. R. Evid. 702, Federal courts must consider five nonexclusive factors in assessing reliability, one of which is the traditional test that looked at whether the principle or method was generally accepted in the relevant scientific community. See Frye v. United States , 293 F. 1013 (D.C. Cir. 1923). “[G]eneral acceptance in the relevant community of the theory and process on which an expert’s testimony is based, on its own, continues to be sufficient to establish the requisite reliability for admission in Massachusetts courts regardless of other Daubert factors.” Commonwealth v. Patterson , 445 Mass. 626, 640 (2005) (latent fingerprint identification theory). See Commonwealth v. Frangipane , 433 Mass. 527, 538 (2001) (Lanigan hearing not necessary where qualified expert testimony has been accepted as reliable in the past in Massachusetts appellate cases). “Where general acceptance is not established by the party offering the expert testimony, a full Daubert analysis provides an alternate method of establishing reliability.” Commonwealth v. Patterson, 445 Mass. at 641. These alternative, Daubert considerations include the ability to test the theory, existence of peer-reviewed publications supporting it, existence of standards for controlling or maintaining it, and known or potential error rates. See Daubert v. Merrell Dow Pharms., Inc., 509 U.S. at 593–594. “A Daubert-Lanigan inquiry does not end once it is determined that an expert’s methodology is generally accepted. In Lightlab Imaging, Inc. v. Axsun Techs., Inc. , 469 Mass. 181, 189–191 (2014), the plaintiff claimed the judge erred in excluding expert witness testimony about lost profits because the witness used the discounted cash flow (DCF) method that is generally regarded as a reliable methodology. However, the judge found a specific aspect of the expert witness’s methodology to be speculative. In particular, the witness relied on a theory known as “first mover advantage,” which posits that “firms that innovate often capture long-term benefits from doing so, thanks to various first mover advantages.” It was within the judge’s discretion to conclude that the use of “first mover advantage” in the witness’s methodology rendered that methodology incapable of being validated and tested. 

In determining reliability, “[a] judge may also look to his own common sense, as well as the depth and quality of the proffered expert’s education, training, experience, and appearance in other courts to determine reliability” (quotation and citation omitted). Commonwealth v. Pasteur , 66 Mass. App. Ct. 812, 826 (2006). See also Commonwealth v. Powell , 450 Mass. 229, 239 (2007) (holding a court may consider an appellate decision from a different jurisdiction). 

In making the reliability determination it is also important that 

“[a] relevant scientific community must be defined broadly enough to include a sufficiently broad sample of scientists so that the possibility of disagreement exists, . . . and . . . trial judges [must] not . . . define the relevant scientific community so narrowly that the expert’s opinion will inevitably be considered generally accepted. In the context of technical forensic evidence, the community must be sufficiently broad to permit the potential for dissent.” 

Commonwealth v. Patterson, 445 Mass. at 643, quoting  Canavan’s Case , 432 Mass. 304, 314 n.6 (2000). See Canavan’s Case, 432 Mass. at 313–316 (holding that the requirement of reliability under Lanigan extends to expert opinions based on personal observations and clinical experience, including medical expert testimony concerning diagnosis and causation). The testimony of a substitute medical examiner who did not perform or witness the autopsy is not, for that reason, unreliable. Commonwealth v. Williams , 475 Mass. 705, 720 (2016).

The requirements of Lanigan, as amplified in Canavan’s Case, do not apply fully as to the standard of care in a medical negligence case.  Palandjian v. Foster , 446 Mass. 100, 108–109 (2006) (“How physicians practice medicine is a fact, not an opinion derived from data or other scientific inquiry by employing a recognized methodology. However, when the proponent of expert testimony incorporates scientific fact into a statement concerning the standard of care, that science may be the subject of a Daubert-Lanigan inquiry.” [Quotation and citation omitted.]). 

The application of the Daubert-Lanigan factors in cases involving the “hard” sciences may not apply in the same way in cases involving the “soft” sciences. See Daubert v. Merrell Dow Pharms., Inc., 509 U.S. at 593–594; Commonwealth v. Lanigan, 419 Mass. at 25–26. See also Mark S. Brodin, Behavioral Science Evidence in the Age of Daubert: Reflections of a Skeptic, 73 U. Cin. L. Rev. 867 (2005). The Supreme Judicial Court has stated as follows: 

“Observation informed by experience is but one scientific technique that is no less susceptible to Lanigan analysis than other types of scientific methodology. The gatekeeping function pursuant to Lanigan is the same regardless of the nature of the methodology used: to determine whether ‘the process or theory underlying a scientific expert’s opinion lacks reliability [such] that [the] opinion should not reach the trier of fact.’  Commonwealth v. Lanigan,  419 Mass. 15, 26 (1994). Of course, even though personal observations are not excepted from Lanigan analysis, in many cases personal observation will be a reliable methodology to justify an expert’s conclusion. If the proponent can show that the method of personal observation is either generally accepted by the relevant scientific community or otherwise reliable to support a scientific conclusion relevant to the case, such expert testimony is admissible.” 

Canavan’s Case, 432 Mass. at 313–314. See, e.g., Commonwealth v. Shanley , 455 Mass. 752, 766 (2010) (“[T]he judge’s finding that the lack of scientific testing did not make unreliable the theory that an individual may experience dissociative amnesia was supported in the record, not only by expert testimony but by a wide collection of clinical observations and a survey of academic literature.”). 

In several cases, the Supreme Judicial Court has relied on the discussion of forensic methods contained in a 2009 report by the National Research Council entitled Strengthening Forensic Science in the United States: A Path Forward 134–135 (2009) (NAS Report). See, e.g., Commonwealth v. Fernandez , 458 Mass. 137, 149 n.17 (2010) (citing NAS Report that the “near universal” laboratory test for drug identity is the “gas chromatography-mass spectrometry” test); Commonwealth v. Barbosa , 457 Mass. 773, 788 n.13 (2010) (citing NAS Report for proposition that nuclear DNA analysis is the standard against which many other forensic individualization techniques are judged). In Commonwealth v. Gambora , 457 Mass. 715, 724–727 (2010), the defendant challenged the scientific basis of the latent fingerprint identification methodology known as ACE-V, which was criticized in the NAS Report. The Supreme Judicial Court observed that “[t]he NAS Report does not conclude that fingerprint evidence is so unreliable that courts should no longer admit it. The Report does, however, stress the subjective nature of the judgments that must be made by the fingerprint examiner at every step of the ACE-V process . . . .” 

The Supreme Judicial Court has not addressed the standard to apply to evidence that meets the general acceptance test but is opposed on grounds that it is nonetheless unreliable. “Given that knowledge is constantly expanding, and that scientific principles are frequently modified in light of new discoveries or theories, it is inconsistent with the reliability requirement to permit any theories or methods to be ‘grandfathered’ as admissible evidence.” M.S. Brodin & M. Avery, Massachusetts Evidence § 7.5.1, at 419 (8th ed. 2007). See Commonwealth v. Camblin , 471 Mass. 639, 650 (2015) (despite statutory authorization, where evidence offered from breathalyzer machine utilizing new methodology not previously shown to be reliable, Lanigan hearing was required).

Fifth Foundation Requirement: Reliability of the Application of the Principle or Method to the Specific Facts of the Case.  See Commonwealth v. Colturi , 448 Mass. 809, 815–817 (2007) (results of otherwise valid breathalyzer test is admissible to establish blood alcohol level at the time of the offense without expert witness testimony on the theory of retrograde extrapolation so long as the test was administered within three hours of the offense); Commonwealth v. McNickles , 434 Mass. 839, 847–850 (2001) (disagreement among experts regarding the reliability of the application of a statistical method known as “likelihood ratios” to mixed samples of DNA evidence went to the weight, but not the admissibility, of the expert witness evidence). But see Lightlab Imaging, Inc. v. Axsun Techs., Inc. , 469 Mass. 181, 192–194 (2014) (the judge did not abuse her discretion in excluding the expert witness’s opinion because the expert’s estimate of lost profits was based on speculation about the availability of future funding for the business); Smith v. Bell Atlantic , 63 Mass. App. Ct. 702, 718–719 (2005) (even though expert witness was qualified and employed a reliable diagnostic method, her lack of knowledge of the details of the patient’s life called into question the reliability of her opinion and justified its exclusion in judge’s discretion). 

Duty to Consult with Expert. In cases where scientific evidence is central to the defense, counsel may have a duty to consult with an appropriate expert. See Commonwealth v. Field, 477 Mass. 553, 556–558 (2017) (error for counsel not to consult with mental health expert regarding defense of mental impairment, but error not likely to have affected verdict). Where science critical to a defense is evolving with new research findings, it may be manifestly unreasonable and present a substantial risk of a miscarriage of justice for counsel to fail to consult or present an expert who could offer evidence in support of the defense. See Commonwealth v. Epps , 474 Mass. 743 (2016) (ineffective assistance of counsel requiring new trial where counsel failed to consult or present expert on possibility of accidental fall as substantial defense in prosecution based upon shaken baby syndrome); Commonwealth v. Millien , 474 Mass. 417 (2016) (failure to consult or call expert on science of shaken baby syndrome).Cf. Commonwealth v. Ayala, 481 Mass. 46, 64 n.20 (2018) (no duty to consult expert in eyewitness identification at time of 2009 trial, when “retention of experts on eyewitness identification was not as prevalent as it is today”).

Profile Evidence. Impermissible “[p]rofile evidence focuses on the characteristics of criminals, while proper expert testimony focuses on the characteristics of crimes.” Commonwealth v. Barrett, 97 Mass. App. Ct. 437, 444 (2020). Using a criminal profile to suggest that a defendant committed an act by comparing him or her to stereotypes is inadmissible as not relevant and inherently prejudicial. Commonwealth v. Day, 409 Mass. 719, 723 (1991) (testimony that defendant fit “child battering” profile inadmissible). Similarly, it is inadmissible for an expert to provide so-called negative profile evidence by testifying that the defendant does not match a particular profile. Commonwealth v. Horne, 476 Mass. 222, 227–228 (2017) (testimony that defendant did not fit description of drug addict and so possessed drugs for purposes of distribution is inadmissible). 

Cross-Reference: Section 404(a), Character Evidence; Crimes or Other Acts: Character Evidence.

Certitude of Expert Witness Opinion. In Commonwealth v. Heang , 458 Mass. 827 (2011), the Supreme Judicial Court explained that when an expert witness offers an opinion that is empirically based but subjective in nature, such as whether a cartridge or casing was fired from a particular firearm, it is not permissible for the witness to imply that the opinion has a statistical or mathematical basis. “Phrases that could give the jury an impression of greater certainty, such as ‘practical impossibility’ and ‘absolute certainty’ should be avoided. The phrase ‘reasonable degree of scientific certainty’ should also be avoided because it suggests that forensic ballistics is a science, where it is clearly as much an art as a science.” (Citation and footnote omitted.) Id. at 849. In Heang, the Supreme Judicial Court provided the following examples of the degree of certitude that an expert witness may express when the opinion is empirically based but subjective in nature: for firearm or ballistics identification, a “reasonable degree of ballistics certainty,” Id. at 848–849; for medical examiner and pathologist opinions, a “reasonable degree of medical certainty,” id. at 849, citing Commonwealth v. Nardi , 452 Mass. 379, 383 (2008); Commonwealth v. DelValle , 443 Mass. 782, 788 (2005); for clinical diagnoses, a “reasonable degree of scientific certainty," Commonwealth v. Roberio ,428 Mass. 278, 280 (1998); and for psychological opinions, a “reasonable degree of psychological certainty,” Commonwealth v. Wentworth , 53 Mass. App. Ct. 82, 86 (2001). It may also be error for a fingerprint expert to state with absolute certainty that a particular latent print matches a known fingerprint. Commonwealth v. Gambora , 457 Mass. 715, 727–728 (2010). In Heang, the court also noted that there are forensic disciplines that permit expert witness opinion to be expressed to a mathematical or statistical certainty. Commonwealth v. Heang, 458 Mass. at 849, citing Commonwealth v. Mattei , 455 Mass. 840, 850–853 (2010) (because it is possible to say to mathematical degrees of statistical certainty that one DNA profile matches another, test results and opinions regarding DNA profile must be accompanied by testimony explaining likelihood of that match occurring in general population). 


Abused Children. See Commonwealth v. Federico , 425 Mass. 844, 847–848 (1997). 

Battered Woman Syndrome. The defendant has a statutory right under G. L. c. 233, § 23F, to present such evidence “where certain specified defenses are asserted.” Commonwealth v. Asenjo, 477 Mass. 599, 607–609 (2017) (“Section 23F is more permissive than the common law bases for expert opinions outlined in Mass. G. Evid. § 703.”).  

Bloodstain Analysis. See Commonwealth v. Vasquez , 462 Mass. 827, 844–846 (2012); Commonwealth v. Powell , 450 Mass. 229, 237–241 (2007). 

Breath Test Analysis. See Commonwealth v. Camblin , 478 Mass. 469, 480 (2017).

Capacity to ContractSee Sparrow v. Demonico , 461 Mass. 322, 327–330 (2012). 

Cause and Origin of Fire. See Commonwealth v. Rosario, 477 Mass. 69, 80–‌81 (2017); Commonwealth v. Goodman , 54 Mass. App. Ct. 385, 389–393 (2002). 

Computer Simulations. Evidence consisting of computer-generated models or simulations is treated like other scientific tests; admissibility is conditioned “on a sufficient showing that: (1) the computer is functioning properly; (2) the input and underlying equations are sufficiently complete and accurate (and disclosed to the opposing party, so that they may challenge them); and (3) the program is generally accepted by the appropriate community of scientists.” Commercial Union Ins. Co. v. Boston Edison Co. , 412 Mass. 545, 549–550 (1992). 

Contribution of Alcohol to Personal Injury. See Baudanza v. Comcast of Mass. I, Inc. , 454 Mass. 622, 631–633 (2009). 

Coprophilia (Sexual Fetish). See Commonwealth v. Lawton , 82 Mass. App. Ct. 528, 538–539 (2012). 

Development of Adolescent Brain. See Commonwealth v. Okoro , 471 Mass. 51, 66–67 (2015) (expert properly permitted to testify regarding development of adolescent brain and how it might affect a particular juvenile’s capacity for impulse control and reasoned decision-making at time in question as it relates to juvenile’s ability to form specific intent for murder but may not opine that no juvenile of that age could form specific intent).

Dissociative Memory Loss. See Commonwealth v. Polk , 462 Mass. 23, 32–36 (2012). 

Dissociative Trance Disorder. See Commonwealth v. Montanez , 55 Mass. App. Ct. 132, 144–146 (2002). 

Distributing Heroin. See Commonwealth v. Miranda , 441 Mass. 783, 792–795 (2004). 

DNA. See Commonwealth v. Dixon , 458 Mass. 446, 453 (2010) (“[a] properly generated DNA profile is a string of code that exclusively identifies a person’s hereditary composition with near infallibility”); Commonwealth v. Mattei ,  455 Mass. 840, 847–852 (2010) (evidence that DNA test failed to exclude defendant “without accompanying evidence that properly interprets that result creates a greater risk of misleading the jury and unfairly prejudicing the defendant than admission of a ‘match’ without accompanying statistics”). There is a distinction between nonexclusion (the defendant is not excluded as a contributor of the sample) and inconclusive (insufficient sample material, contamination, or some other problem) DNA results. “Evidence that a defendant is not excluded could suggest to the jury that a link would be more firmly established if only more [sample] were available for testing. Such evidence should not [be] admitted without accompanying statistical explanation of the meaning of nonexclusion.” Commonwealth v. Cameron , 473 Mass. 100, 106 (2015); Commonwealth v. Lally , 473 Mass. 693, 702–704 (2016). But see Commonwealth v. Lester, 486 Mass. 239, 247 (2020) (admission of DNA charts not error but “the better course is to remind the jury that they must consider the charts in conjunction with the expert’s testimony, including the expert’s statistical analysis”). Inconclusive DNA results are not relevant absent a Bowden defense.  Commonwealth v. Cameron, 473 Mass. at 107 n.8. See Section 1107, Inadequate Police Investigation Evidence

Effect of Intoxicants. See Commonwealth v. Sherman, 481 Mass. 464, 477–478 (2019) (evidence of drug use to challenge witness’s ability to perceive and remember must be supported by expert testimony where connection between drug use and witness’s ability to perceive, remember, or testify to event is not generally known). See also Commonwealth v. Hernandez, 481 Mass. 189, 194 (2019) (question put to lay witness concerning how a person reacts to heroin withdrawal improper because it required specialized knowledge).

Extrapolation. Extrapolation evidence to determine the weight of drugs is permissible, and any objections to its admissibility should be raised by way of pretrial motion. Commonwealth v. Crapps , 84 Mass. App. Ct. 442, 445–449 (2013). 

False Confessions. See Commonwealth v. Hoose , 467 Mass. 395, 413–420 (2014). 

Field Testing Drugs. See Commonwealth v. Fernandez, 458 Mass. 137, 151 (2010); Commonwealth v. Rodriguez, 92 Mass. App. Ct. 774, 779–780 (2018).

Fingerprints. See Commonwealth v. Patterson , 445 Mass. 626, 641–655 (2005). See also Commonwealth v. Joyner , 467 Mass. 176, 177 (2014) (testimony of fingerprint expert did not violate prohibition against expressing an opinion to a scientific certainty that there was a match). Where a fingerprint is the only identification evidence, the Commonwealth must prove beyond a reasonable doubt that the fingerprint was placed during the commission of the charged crime. Commonwealth v. French, 476 Mass. 1023, 1024–1025 (2017). Unlike DNA evidence, the statistical significance of an opinion about a match is not a foundational requirement, but may affect the weight of the evidence. Commonwealth v. Wadlington , 467 Mass. 192 (2014). Cf. Commonwealth v. Gambora ,  457 Mass. 715, 724–725 (2010) (considering report by National Research Council, Strengthening Forensic Science in the United States: A Path Forward 102–104, 136–145 [2009]). 

Firearm Identification (Forensic Ballistics). See Commonwealth v. Heang , 458 Mass. 827, 847–848 (2011) (adopting “guidelines” for the admissibility of expert firearm identification testimony that [1] require documentation of the basis of the expert’s opinion before trial, which the Commonwealth must disclose to the defense in discovery; [2] require an explanation by the expert to the jury of the theories and methodologies underlying the field of forensic ballistics before offering any opinions; and [3] limit the degree of certitude that the qualified expert may express about whether a particular firearm fired a specific projectile or cartridge to a “reasonable degree of ballistic certainty”). 

Gang Membership. See Commonwealth v. Barbosa, 477 Mass. 658, 667–669 (2017).

Gunshot Residue. See Commonwealth v. Johnson , 463 Mass. 95, 107–108 (2012);  Commonwealth v. Heang , 458 Mass. 827, 851 (2011). 

Personality Testing. See Ready, petitioner , 63 Mass. App. Ct. 171, 172–179 (2005). 

Posttraumatic Stress Disorder. See Commonwealth v. Anestal , 463 Mass. 655, 658 n.5 (2012); Commonwealth v. Crawford , 429 Mass. 60, 67 (1999). 

Retrograde Extrapolation. See Commonwealth v. Senior, 433 Mass. 453, 458–462 (2001). But see Commonwealth v. Dacosta, 85 Mass. App. Ct. 386, 386–388 (2014) (breath test within fifty minutes of arrest permits inference of blood alcohol content above 0.08 percent without need for expert witness testimony). 

Sex Offender Registry Board. See John Doe, Sex Offender Registry Bd. No. 234076 v. Sex Offender Registry Bd., 484 Mass. 666, 673–674 (2020) (expert testimony admissible in classification hearings unless it is irrelevant, unreliable, or repetitive).

Sexual Assault Evidence. See Commonwealth v. Scesny, 472 Mass. 185, 194–196 (2015) (testimony regarding what evidence criminologist would expect to have found if victim pulled up her underwear and pants following intercourse).

Sexually Dangerous Persons. See Commonwealth v. George, 477 Mass. 331, 341–342 (2017) (Static-99R risk assessment tool’s raw score and risk percentage are admissible; Static-99R risk category labels are inadmissible, as they do not provide sincere, numeric estimates of recidivism risk);  Commonwealth v. Ortiz, 93 Mass. App. Ct. 381, 389 (2018) (no abuse of discretion in excluding penile plethysmograph [PPG] examination results on issue of likelihood of sexual reoffense).

Shaken Baby Syndrome. See Commonwealth v. Epps , 474 Mass. 743 (2016); Commonwealth v. Millien , 474 Mass. 417 (2016).

Susceptibility to Suggestiveness. See Commonwealth v. Soares , 51 Mass. App. Ct. 273, 280–282 (2001). 

Valuation of Business Interest. In divorce cases, the judge may accept one expert valuation over another or reject expert opinion altogether and arrive at a valuation on other evidence, but he or she may not reach a valuation that varies from the requirements of the equitable distribution statute. G. L. c. 208, § 34 . See Adams v. Adams , 459 Mass. 361, 380–381 (2011); Bernier v. Bernier , 449 Mass. 774 (2007). 

Valuation of Real Estate. There is no requirement that the person testifying as an expert have sales or practical experience in the locality about which they are testifying. See McLaughlin v. Board of Selectman of Amherst , 422 Mass. 359, 362–363 (1996). A real estate broker or appraiser with “sufficient experience and knowledge of values of other similar real estate in the particular locality” may testify. Lee Lime Corp. v. Massachusetts Turnpike Auth. , 337 Mass. 433, 436 (1958). A witness who had “worked as an appraiser” and “was in the process of earning professional designations in the appraisal field” may testify as an expert in real estate. See Lavin v. Lavin , 24 Mass. App. Ct. 929, 931 (1987). An expert witness may use the depreciated reproduction cost method to form an opinion as to the value of real estate when the judge finds that there is a justification for the use of this disfavored approach. Correia v. New Bedford Redev. Auth. , 375 Mass. 360, 362–367 (1978). 

For examples of cases applying this section, see M.S. Brodin & M. Avery, Massachusetts Evidence §§ 7.4–7.6 (2018 ed.); 2 M.G. Perlin & D. Cooper, Proof of Cases in Massachusetts §§ 71:1–71:23 (2017–2018 ed.); and W.G. Young, J.R. Pollets, & C. Poreda, Annotated Guide to Massachusetts Evidence § 702 (2017–2018 ed.).

Jury Instructions. See Commonwealth v. Hinds , 450 Mass. 1, 12 n.7 (2007). 

Cross-Reference: Section 703, Bases of Opinion Testimony by Experts.

Section 703. Bases of opinion testimony by experts

The facts or data in the particular case upon which an expert witness bases an opinion or inference may be those perceived by or made known to the witness at or before the hearing. These include (a) facts observed by the witness or otherwise in the witness’s direct personal knowledge; (b) evidence already in the record or that will be presented during the course of the proceedings, which facts may be assumed to be true in questions put to the witness; and (c) facts or data not in evidence if the facts or data are independently admissible in evidence and are a permissible basis for an expert to consider in formulating an opinion.


This section is derived from Department of Youth Servs. v. A Juvenile , 398 Mass. 516, 531 (1986); LaClair v. Silberline Mfg. Co. , 379 Mass. 21, 32 (1979); and Commonwealth v. Russ , 232 Mass. 58, 73 (1919). See Commonwealth v. Piantedosi, 478 Mass. 536, 541–546 (2017). Massachusetts law differs from Fed. R. Evid. 703, or Proposed Mass. R. Evid. 703, which permits opinions based on inadmissible evidence if it is of a type reasonably relied upon by experts in the relevant field. See Commonwealth v. Waite, 422 Mass. 792, 803 (1996) (“When an expert provides the jury with an opinion regarding the facts of the case, that opinion must rest on a proper basis, else inadmissible evidence might enter in the guise of expert opinion. The expert must have knowledge of the particular facts from firsthand observation, or from a proper hypothetical question posed by counsel, or from unadmitted evidence that would nevertheless be admissible.”). Thus, a psychologist called by the defense in a murder trial could opine on the defendant’s mental impairment at the time of the offense based on the witness’s interview with the defendant five weeks after the killings and the contents of police and medical records, but not on the basis of a psychiatrist’s earlier “preliminary diagnosis” that was not shown to be reliable and independently admissible. Commonwealth v. Waite, 422 Mass. at 803–804. See also Vassallo v. Baxter Healthcare Corp., 428 Mass. 1, 15–16 (1998) (“The judge properly prevented the [parties’] experts from testifying on direct examination to the out-of-court opinions of other scientists in the absence of some specific exception to the hearsay rule.”). But see Commonwealth v. Asenjo, 477 Mass. 599, 607–609 (2017) (error to exclude expert testimony regarding battered woman syndrome where G. L. c. 233, § 23F, provides independent statutory basis for admission of evidence; statute is more permissive than common law embodied in Section 703 and permits expert testimony based solely on defendant’s assertion of certain specified defenses).

On direct examination, the expert witness’s testimony regarding the basis of his or her opinion is limited to (1) facts within the witness’s personal knowledge; (2) facts in evidence; or (3) with approval of the court, facts that a party will put in evidence. However, “it is settled that an expert witness may not, under the guise of stating the reasons for his opinion, testify to matters of hearsay in the course of his direct examination unless such matters are admissible under some statutory or other recognized exception to the hearsay rule.” Commonwealth v. Nardi, 452 Mass. 379, 392 (2008), quoting Grant v. Lewis/Boyle, Inc. , 408 Mass. 269, 273 (1990). See Matter of J.P., 486 Mass. 117, 122 n.11 (2020) (on direct examination, expert may not testify about statements within medical record that formed basis of expert’s opinion where record itself was not admitted). The limitation on the direct-examination testimony of expert witnesses operates in both civil and criminal cases and applies to both sides. Commonwealth v. Chappell, 473 Mass. 191, 204 (2015) (this evidentiary rule does not violate defendant’s right to present a full defense). On cross-examination, the opposing party may choose to elicit the underlying facts or data. See Section 705.

An expert may base an opinion on facts within the expert’s personal knowledge. Compare Commonwealth v. Barbosa, 477 Mass. 658, 667–669 (2017) (expert properly testified, based on personal knowledge, that defendant belonged to gang), with Commonwealth v. Wardsworth, 482 Mass. 454, 466–470 (2019) (reversible error for expert to testify that defendant was gang member based solely on personal observations that defendant associated with suspected gang members).

Unless the evidence is capable of only one interpretation, the question to the expert witness must refer to specific portions of the record. See Connor v. O’Donnell, 230 Mass. 39, 42 (1918).

In determining whether facts or data are independently admissible, the court must determine whether the underlying facts or data would potentially be admissible in any form through appropriate witnesses. Such witnesses need not be immediately available in court to testify. See Commonwealth v. Markvart, 437 Mass. 331, 337–338 (2002). But see Custody of Michel, 28 Mass. App. Ct. 260, 265–267 (1990) (permitting broader basis for testimony and reports of court-appointed investigators under G. L. c. 119, § 24).

Cross-Reference: Section 705, Disclosure of Facts or Data Underlying Expert Opinion

Limitation on Cross-Examination. On cross-examination of an expert, a judge may exclude evidence as unfairly prejudicial, see Section 403, even if the expert is aware of those facts, if the facts were not relied upon as part of the expert’s opinion, do not clarify or discredit the opinion, and serve only to focus the jury on those facts. Commonwealth v. Anestal , 463 Mass. 655, 667–668 (2012) (prior bad acts excluded). 

Risk of Inaccurate Forensic Analysis. Common-law rules of evidence are intended to minimize the risk of inaccurate forensic analysis in various ways:

“Where there is reason to believe that evidence has been mislabeled or mishandled or that data have been fabricated or manipulated, a defendant may challenge the admissibility of an expert opinion relying on such evidence or data in a Daubert-Lanigan hearing, because an opinion must rest on evidence or data that provide ‘a permissible basis’ for an expert to formulate an opinion. A defendant may also challenge the admissibility of an opinion where an expert relies solely on the conclusions of the testing analyst, without knowledge of the procedures employed by the testing analyst or the underlying data and evidence that are generally contained in worksheets, because a conclusory opinion alone may not be a permissible basis on which an expert may rest an opinion. Where an expert opinion survives a Daubert-Lanigan challenge or where . . . the defendant does not challenge the admissibility of the expert’s opinion, the defendant may still . . . cross-examine the testifying expert as to the risk of evidence being mishandled or mislabeled or of data being fabricated or manipulated, and as to whether the expert’s opinion is vulnerable to these risks.” (Citations omitted.)

Commonwealth v. Barbosa, 457 Mass. 773, 790–791 (2010).

Substituted Experts. Hearsay statements of fact and opinion contained in forensic reports—such as drug certificates, autopsy reports, and DNA analyses—created to be used against the accused in investigating or prosecuting a crime are inadmissible unless the author is present in court and subject to cross-examination or there was a prior opportunity for cross-examination. Melendez-Diaz v. Massachusetts, 557 U.S. 305, 309–311 (2009); Commonwealth v. Nardi, 452 Mass. 379, 391–394 (2008). However, a “substitute expert,” that is, an expert witness who did not author or create the report, may testify to his or her own opinion based on the tests and data contained in another analyst’s report, so long as the substitute expert does not testify to or assert the truth of the author’s statements, observations, or opinions. See Commonwealth v. Grady, 474 Mass. 715, 716 (2016) (substitute chemist/drug analyst); Commonwealth v. Chappell, 473 Mass. 191, 201–202 (2015) (substitute DNA analyst); Commonwealth v. Nardi, 452 Mass. 379, 387–394 (2008) (substitute medical examiner).

Meaningful Opportunity to Cross-ExamineThe Massachusetts common law of evidence is more protective of confrontation rights than the Sixth Amendment to the United States Constitution in that it requires that the defendant have “a meaningful opportunity to cross-examine the expert about her opinion and the reliability of the facts or data that underlie her opinion.” Commonwealth v. Tassone , 468 Mass. 391, 399–402 (2014). Thus, in Tassone, the court held that where the substitute DNA analyst was not affiliated with the laboratory where the DNA testing was conducted and there was no showing that she had any personal knowledge of that lab’s evidence-handling protocols, the defendant was denied the opportunity to explore through cross-examination whether the testing was flawed. The court distinguished Commonwealth v. Greineder, 464 Mass. 580 (2013), where the substitute DNA expert was the forensic laboratory director of the facility where the DNA testing was conducted and was personally aware of the DNA testing process employed by the laboratory. See also Commonwealth v. Barry, 481 Mass. 388, 407–408 (2019) (director of laboratory that conducted DNA testing was not substitute expert, despite not being person who physically tested samples, because he participated in analysis of samples and testified about report detailing his conclusions). Compare Commonwealth v. Sanchez, 476 Mass. 725, 734 (2017) (fire inspector who was present for electrician’s inspection of arson site could testify and be meaningfully cross-examined about his own observations), with Commonwealth v. Jones, 472 Mass. 707, 715–716 (2015) (where DNA expert’s knowledge of how DNA samples had been collected was derived from form completed by person who had collected the specimens from victim’s body, no meaningful opportunity to cross-examine witness).

DNA Analyst. Where the prosecution offers an opinion about a DNA profile match, “a meaningful opportunity for cross-examination means that a defendant must have the opportunity substantively to explore the ‘risk of evidence being mishandled or mislabeled, or of data being fabricated or manipulated, and . . . whether the expert’s opinion is vulnerable to these risks.’” Commonwealth v. Tassone, 468 Mass. 391, 400 (2014), quoting Commonwealth v. Barbosa, 457 Mass. 773, 791 (2010). If the prosecution does not call the DNA analyst who conducted the testing as a witness, it must, at a minimum, call an expert affiliated with the laboratory where the testing took place. Commonwealth v. Tassone, 468 Mass. at 402. Where the testifying expert has personal knowledge of the testing laboratory’s procedures, the witness may give an opinion about a DNA match, even though the basis is in whole or in part evidence collected or created by an absent DNA analyst. See Commonwealth v. Greineder, 464 Mass. 580, 583–584 (2013). An expert who has no knowledge of how the sample was collected cannot testify to the location from which the sample was collected. Commonwealth v. Jones, 472 Mass. 707, 716–717 n.3 (2015) (no meaningful opportunity to cross-examine testifying DNA expert about how specimen was collected).

Medical Examiner. In accordance with Section 705, a substitute medical examiner may testify to his or her opinion even though it is based in whole or in part on evidence collected or created by the absent medical examiner. See Commonwealth v. Seino, 479 Mass. 463, 466–468 (2018) (substitute medical examiner may offer opinion as to cause of death based upon review of independently admissible documents contained in original medical examiner’s file); Commonwealth v. Nardi, 452 Mass. 379, 388 (2008). The original autopsy report, notes, and photographs provide the defendant with a “meaningful opportunity” to cross-examine the substitute witness about possible flaws in his or her opinion. Commonwealth v. Tassone, 468 Mass. 391, 400 (2014). The Commonwealth is not required to show that the medical examiner who performed an autopsy is unavailable for a substitute medical examiner to testify. Commonwealth v. Leiva, 484 Mass. 766, 792 (2020).

Cross-Reference: Section 702, Testimony by Expert WitnessesSection 705, Disclosure of Facts or Data Underlying Expert OpinionIntroductory Note to Article VIII, Hearsay.

Section 704. Opinion on ultimate issue

An opinion is not objectionable just because it embraces an ultimate issue.


This section is derived from Proposed Mass. R. Evid. 704; Commonwealth v. Woods , 419 Mass. 366, 374–375 (1995); and Simon v. Solomon , 385 Mass. 91, 105 (1982). The critical question is not whether the opinion touches on the ultimate issue, but whether it satisfies Sections 403, Excluding Relevant Evidence for Prejudice, Confusion, Waste of Time, or Other Reasons ; 701, Opinion Testimony by Lay Witnesses702, Testimony by Expert Witnesses; and any other applicable sections. See Commonwealth v. Goddard, 476 Mass. 443, 446–447 (2017); Commonwealth v. Canty , 466 Mass. 535, 543 (2013); Martel v. Massachusetts Bay Transp. Auth. , 403 Mass. 1, 3–4 (1988); Commonwealth v. LaCorte , 373 Mass. 700, 705 (1977); Commonwealth v. Almeida , 34 Mass. App. Ct. 901, 902–903 (1993); Commonwealth v. Lopes , 25 Mass. App. Ct. 988, 990 (1988), citing Commonwealth v. Sendele , 18 Mass. App. Ct. 755, 760 (1984). Accord M.S. Brodin & M. Avery, Massachusetts Evidence § 7.3.2 (2018 ed.). 

At least four different, but related, reasons are given for the exclusion of opinion evidence on an ultimate issue. First, such opinions offer no assistance to the fact finders “because the jury are capable of making that assessment without an expert’s aid.” Commonwealth v. Colin C., 419 Mass. 54, 60 (1994). See Commonwealth v. Andujar, 57 Mass. App. Ct. 529, 531 (2003). Second, “[o]n such questions, the influence of an expert’s opinion may threaten the independence of the jury’s decision.” Simon v. Solomon, 385 Mass. 91, 105 (1982). Third, such questions call for opinions on matters of law or mixed questions of law and fact, and the jury must be allowed to draw their own conclusions from the evidence. See Commonwealth v. Hesketh, 386 Mass. 153, 161–162 (1982). Fourth, expert opinion in the form of conclusions about the credibility of a witness or a party are beyond the scope of the witness’s expertise and in the realm of speculation and conjecture. See Commonwealth v. Gardner, 350 Mass. 664, 666 (1966).

Improper Vouching. Expert witness testimony which simply amounts to an opinion on the credibility of a witness is inadmissible as improper vouching; credibility is an issue reserved for the jury that does not require the assistance of an expert. This issue commonly arises in sexual abuse cases, in which an expert witness may testify to general characteristics to assist the jury’s understanding, but may not compare the alleged victim to those characteristics. Commonwealth v. Richardson, 423 Mass. 180, 185–186 (1996), quoting Commonwealth v. Trowbridge, 419 Mass. 750, 759 (1995) (“[a]lthough expert testimony on the general behavioral characteristics of sexually abused children is permissible, an expert may not refer or compare the child to those general characteristics”). See Commonwealth v. Jewett, 442 Mass. 356, 368 (2004) (“in the absence of special circumstances, an expert may not be asked whether a rape or sexual assault has occurred”). Testimony about profiling is generally inadmissible. Commonwealth v. Coates, 89 Mass. App. Ct. 728, 733–737 (2016) (trial judge properly excluded criminal-profile testimony that defendant did not fit profile of pedophile); Commonwealth v. Aspen, 85 Mass. App. Ct. 278, 282–284 (2014), citing Commonwealth v. Federico, 425 Mass. 844, 849 (1997) (conviction reversed where expert gave profile testimony relating to intrafamilial sexual abuse that closely resembled complainant’s family makeup and dynamic).

Testimony by an expert who has also treated the victim must be carefully scrutinized to avoid the implication that the expert’s contact with the victim gives the expert special knowledge about credibility. See Commonwealth v. Quinn, 469 Mass. 641, 646 (2014) (risk of improper vouching was “especially acute” because expert witness had treated victim for months); Commonwealth v. Trowbridge, 419 at 759–760. The rule against vouching does not prohibit an expert from explaining physical findings or characteristics and their significance, See, e.g., Commonwealth v. Alvarez, 480 Mass. 299, 314 (2018) (general statements by treating physician that it is “very uncommon” to find physical genital injury in sexual abuse victim and that “absence of physical trauma is not inconsistent with abuse” do not constitute implicit vouching). Cf. Commonwealth v. Burgess, 450 Mass. 422, 436 (2008) (“the prosecutor [improperly] asked [the Commonwealth’s expert] to comment on the credibility of the Commonwealth’s theory of the case by asking whether its theory was ‘consistent’ with [the expert’s] observations”).

Illustrations. For examples of cases applying this section, see M.S. Brodin & M. Avery, Massachusetts Evidence § 7.3 (2018 ed.); and 2 M.G. Perlin & D. Cooper, Proof of Cases in Massachusetts § 71.4 (2017–2018 ed.). 

Operating Under the Influence Cases. In Commonwealth v. Canty , 466 Mass. 535, 541 (2013), the court explained that the limitation on testimony that amounts to an opinion as to guilt or innocence applies to the lay witness as well as to the expert witness. Cross-Reference: Section 701, Opinion Testimony by Lay Witnesses.

Opinions About the Law Versus the Facts. Legal questions, as to which testimony is not permitted, should be distinguished from factual conclusions, as to which testimony is proper. The line between a “conclusion of law” and an “ultimate factual issue” is sometimes blurred. Commonwealth v. Little , 453 Mass. 766, 769 (2009) (“Narcotics investigators may testify as experts to describe how drug transactions occur on the street . . . [such as] testimony on the use of lookouts in drug transactions, and the significance of the purity of seized drugs. We have also repeatedly held that there is no error in allowing a police detective to testify that in his opinion the amount of drugs possessed by the defendant was not consistent with personal use but was consistent with an intent to distribute.” [Citations and quotations omitted.]). See Commonwealth v. Roderiques , 78 Mass. App. Ct. 515, 522 (2010) (pediatrician allowed to testify that baby’s injuries were not accidental); Puopolo v. Honda Motor Co. , 41 Mass. App. Ct. 96, 99 (1996) (expert should have been permitted to testify that vehicle was unreasonably dangerous even though special question given to jury was framed in nearly identical language). Cf. Commonwealth v. Brady , 370 Mass. 630, 635 (1976) (insurance agent may not testify to applicability of insurance coverage); Perry v. Medeiros , 369 Mass. 836, 842 (1976) (building inspector cannot give opinion interpreting building code); Commonwealth v. Coleman , 366 Mass. 705, 711 (1975) (medical examiner not permitted to testify that death was “homicide”); DeCanio v. School Comm. of Boston , 358 Mass. 116, 125–126 (1970) (expert could not testify that “suspension and dismissal of probationary teachers without a hearing ‘would have no legitimate educational purpose’”); Commonwealth v. Gardner , 350 Mass. 664, 666–667 (1966) (doctor in rape prosecution cannot testify to “forcible entry”); S.D. Shaw & Sons v. Joseph Rugo, Inc. , 343 Mass. 635, 639 (1962) (witness may not give opinion as to whether certain work was included in contract specification); Commonwealth v. Ross , 339 Mass. 428, 435 (1959) (guilt); Foley v. Hotel Touraine Co. , 326 Mass. 742, 745 (1951) (treasurer of corporation could not testify on question whether assistant manager had “ostensible authority” on day of accident); Silva v. Norfolk & Dedham Mut. Fire Ins. Co., 91 Mass. App. Ct. 413, 420 (2017) (testimony in action brought under G. L. c. 176D that insurer’s action was “unfair and deceptive” properly excluded). But see Ford v. Boston Hous. Auth. , 55 Mass. App. Ct. 623, 626 (2002) (expert testimony explaining requirements of complicated code was not per se inadmissible; judge had discretion to admit expert opinion of building inspector that “if the door was locked at the time of the accident . . . that would have been noncompliance with the State building code”).

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.


This section is 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 (2013). However, on cross-‌examination, the opposing party may choose to elicit the hearsay basis for an opinion offered on direct examination. See Commonwealth v. Nardi , 452 Mass. 379, 387–395 (2008). In Commonwealth v. Barbosa , 457 Mass. 773, 785–787 (2010), 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); Commonwealth v. Nardi , 452 Mass. 379, 387–395 (2008).

Cross-Reference: 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.

Section 706. Court-appointed experts

(a) Appointment. If legally permissible, the court, on its own or at the request of a party, may appoint an expert. Unless mandated by law to accept the assignment, the expert shall have the right to refuse such appointment. The court, after providing an opportunity to the parties to participate, shall inform the expert of his or her duties. The expert may be required to testify.

(b) Compensation. Expert witnesses so appointed are entitled to reasonable compensation, as set by the court, unless controlled by statute or rule. Except as otherwise provided by law, the compensation shall be paid by the parties in such proportion and at such time as the court directs, and thereafter charged in like manner as other costs.

(c) Disclosure of appointment. The fact that the court appointed the expert witness shall not be disclosed to the jury.

(d) Parties’ choice of their own experts. This section does not limit a party in calling its own experts.


This section is derived from Commonwealth v. O’Brien , 423 Mass. 841, 855 n.24 (1996); Fed. R. Evid. 706; and Proposed Mass. R. Evid. 706, and reflects the Massachusetts practice of making widespread use of court appointed experts. See, e.g., G. L. c. 119, §§ 21 24 (court appointed expert to assist in determination of cases involving children in need of services); G. L. c. 123, § 15(a)–(c) (court appointed expert to assess criminal defendant’s competency to stand trial or criminal responsibility); G. L. c. 123, § 15(e) (court appointed expert to render opinion to assist court in sentencing defendant); G. L. c.190B, § 5-303(e) (court appointed expert to assess mental health of a person who may be in need of guardianship); G. L. c. 215, § 56A (guardian ad litem to investigate facts for the Probate and Family Court relating to care, custody, and maintenance of children); Brodie v. Jordan , 447 Mass. 866, 867 (2006) (expert witness appointed by court to render opinion on the value of corporation’s net assets); Commonwealth v. Berry , 420 Mass. 95, 103 (1995) (judge warranted in relying upon opinion of court appointed expert); Commonwealth v. Aponte , 391 Mass. 494, 497–498 (1984) (court appointed expert in statistical analysis in social sciences to assist in resolution of challenge to method of grand jury selection in Essex County); Gilmore v. Gilmore , 369 Mass. 598, 604–‌605 (1976) (use of court appointed guardian ad litem for investigation in child custody cases); Munshani v. Signal Lake Venture Fund II, LP , 60 Mass. App. Ct. 714, 717 (2004) (court appointed expert to assess authenticity of an electronic communication).

Failure to seek funds to consult or retain an expert where there is new scientific research and the science is evolving, which could provide a substantial ground of defense, may constitute ineffective assistance of counsel. Commonwealth v. Millien , 474 Mass. 417 (2016) (failure to consult or call expert on shaken baby syndrome).

Downloads for Article VII: Opinion and expert evidence



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