In Commonwealth v. Hinds, issued today, the Supreme Judicial Court reversed the conviction of a man convicted of first degree murder because of a faulty jury instruction on the evaluation of expert testimony. In the opinion, the court goes on to question the instruction previously "cited with approval" in Commonwealth v. Rodriguez, 437 Mass. 554 (2002) from Section 4.7.1. of the Massachusetts Superior Court Criminal Practice Jury Instructions (Mass. Continuing Legal Educ. 1999). The SJC then provides this "better 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."