Jury instructions regarding witnesses in Massachusetts are outlined in Massachusetts’s Superior Court Civil Practice Jury Instructions, §1.2.8. MASS. SUP. CT. CIVIL PRACTICE JURY INSTR. § 1.2.8 (2016). There is not a separate rule for expert witnesses, but §1.2.8 applies to all witnesses. Id. This rule instructs the jury to decide what witnesses to believe and how much weight to give each witness’s testimony. Id. Also, if two experts testify to conflicting opinions or analyses, it is up to the jury to determine which they deem more credible and trustworthy. Id. Further, the jury can either believe or disregard a witness’s testimony depending on how the jury views the testimony in light of all the evidence presented. Id. The jury is to consider the “witness’s character, appearance and demeanor on the witness stand, frankness or lack of frankness in testifying, whether testimony is reasonable or unreasonable, probable or improbable” to gauge how much credibility to afford each expert witness. Id.
