Instruction 3.640, Criminal Model Jury Instructions for Use in the District Court

EXPERT WITNESS

When a case involves a technical issue, a person with special training

or experience in that technical field is permitted to give his or her opinion

about that technical issue, in order to help you as the jury.

Merely because a witness has expressed an opinion, however, does

not mean that you must accept that opinion. In the same way as with any

other witness, it is up to you to decide whether to rely on it. You may

accept it or reject it, and give it as much weight as you think it deserves. In

making your assessment, you may consider the witness’s education and

experience, the reasons given for the opinion, and all the other evidence in

the case.

Commonwealth v. Montecalvo, 367 Mass. 46, 54, 323 N.E.2d 888, 893 (1975); Commonwealth v.

Costa, 360 Mass. 177, 183, 274 N.E.2d 802, 806 (1971); Commonwealth v. Smith, 357 Mass. 168,

178, 258 N.E.2d 13, 19-20 (1970). Manual of Model Jury Instructions for the Ninth Circuit § 4.16

(1985 ed.); Committee on Pattern Jury Instructions, District Judges Ass'n of the Eleventh Circuit,

Pattern Jury Instructions—Criminal Cases § 7 (1985 ed.). As to when expert testimony is appropriate,

see Jury Trial Manual for Criminal Offenses Tried in the District Court § 2.46. Language from the

instruction approved in Commonwealth v. Rodriguez, 437 Mass. 554, 561, 773 N.E.2d 946 (2002),

should be used with caution because its repeated use of the word “true” could invite speculation about

the standard of proof for determining whether facts are “true.” Commonwealth v. Hinds, 450 Mass.

1, 875 N.E.2d 488 (2007).

The assessment of an expert witness’s qualifications is shared by the judge and the jury. The judge

must make a preliminary finding that the proffered witness is at least minimally qualified to testify as

an expert, and may not abdicate that responsibility to the jury. The jury must then assess the

soundness and credibility of the expert’s opinion, and one factor in that assessment is the extent of

the expert’s knowledge and experience. The model instruction avoids the word “expert,” since it may

prejudice the jury’s ultimate responsibility to accept or reject the witness’s expertise. Leibovich v.

Antonellis, 410 Mass. 568, 572-573, 574 N.E.2d 978, 982 (1991).

ALTERNATE INSTRUCTION

There is one more point about witnesses to address:

expert witnesses. This term refers to witnesses who have

specialized training or experience in a particular field.

Generally, in cases that are tried in our courts, both civil and

criminal, witnesses may testify only to facts that are within their

own personal knowledge — that is, things that they have

personally seen or heard or felt. However, in a variety of cases,

issues arise that are beyond the experience of lay persons, and

in those types of cases, we allow a person with specialized

training or experience, called an expert witness, to testify, and to

testify not only to facts, but also to opinions, and the reasons for

his or her opinions, on issues that are within the witness’s field

of expertise and are relevant and material to the case.

Because a particular witness has specialized training and

experience in his or her field does not put that witness on a

higher level than any other witness, and you are to treat the

so-called expert witness just like you would treat any other

witness. In other words, as with any other witness, it is

completely up to you to decide whether you accept the

testimony of an expert witness, including the opinions that the

witness gave. It is also entirely up to you to decide whether you

accept the facts relied on by the expert and to decide what

conclusions, if any, you draw from the expert’s testimony. You

are free to reject the testimony and opinion of such a witness, in

whole or in part, if you determine that the witness’s opinion is

not based on sufficient education and experience or that the

testimony of the witness was motivated by some bias or interest

in the case. You must also, as has been explained, keep firmly

in mind that you alone decide what the facts are. If you

conclude that an expert’s opinion is not based on the facts, as

you find those facts to be, then you may reject the testimony and

opinion of the expert in whole or in part.

You must remember that expert witnesses do not decide

cases; juries do. In the last analysis, an expert witness is like

any other witness, in the sense that you alone make the

judgment about how much credibility and weight you give to the

expert’s testimony, and what conclusions you draw from that

testimony.

Commonwealth v. Hinds, 450 Mass. 1, 875 N.E.2d 488 (2007) (recommending

this model instruction as preferable to the standard Superior Court instruction

approved in Commonwealth v. Rodriguez, 437 Mass. 554, 561, 773 N.E.2d 946

[2002]).

SUPPLEMENTAL INSTRUCTION

Assumed facts. Members of the jury, you will have noticed

that this witness offered you an opinion that was based on

certain assumed facts. It is permissible for a witness to testify

in that form, because it is your responsibility — and not the

witness’s — to determine from all the evidence what the facts

are.

Obviously, such an opinion is of use to you only if the facts

which the witness has been asked to assume, and on which his

(her) opinion is based, are in fact true.

If you find that one or more significant facts that the

witness was asked to base his (her) opinion upon are not true,

then his (her) opinion is not relevant to the facts of this case,

and you should not consider his (her) opinion in your

deliberations.

Commonwealth v. Bjorkman, 364 Mass. 297, 306, 303 N.E.2d 715, 721 (1973);

Commonwealth v. Taylor, 327 Mass. 641, 649, 100 N.E.2d 22, 26-27 (1951). See

Bagge’s Case, 369 Mass. 129, 134, 338 N.E.2d 348, 352 (1975); Wing v.

Commonwealth, 359 Mass. 286, 287-288, 268 N.E.2d 658, 659-660 (1971);

Commonwealth v. Ward, 14 Mass. App. Ct. 37, 41-42, 436 N.E.2d 439, 443 (1982).

An expert opinion may be based either on facts or data in evidence or “on facts or

data not in evidence if the facts or data are independently admissible and are a

permissible basis for an expert to consider in formulating an opinion.” Allowing an

opinion to be based on admissible but not actually admitted facts “eliminate[s] the

necessity of producing exhibits and witnesses whose sole function is to construct a

proper foundation for the expert’s opinion.” Department of Youth Servs. v. A

Juvenile, 398 Mass. 516, 531-532, 499 N.E.2d 812, 821 (1986).

“If a party believes that an expert is basing an opinion on inadmissible facts or data,

the party may request a voir dire to determine the basis of the expert opinion.” Id.

Absent a request for advance voir dire, the witness may offer the jury an expert

opinion without disclosing the facts on which it is based, but the other party has the

right to explore those facts on cross-examination. This has eliminated the

requirement that the proponent elicit expert testimony only through hypothetical

questions. Id.