(a) Stating an Opinion Without Disclosing the Underlying Facts or Data. 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.
(b) Voir Dire Examination of an Expert About the Underlying Facts or Data. Before an expert states an opinion or discloses the underlying facts or data, an adverse party in a civil case may—or in a criminal case must—be permitted to examine the expert about the underlying facts or data. This examination must take place outside the jury’s hearing.
(c) Admissibility of Opinion. An expert’s opinion is inadmissible if the underlying facts or data do not provide a sufficient basis for the opinion.
(d) When Otherwise Inadmissible Underlying Facts or Data May Be Disclosed; Instructing the Jury. If the underlying facts or data would otherwise be inadmissible, the proponent of the opinion may not disclose them to the jury if their probative value in helping the jury evaluate the opinion is outweighed by their prejudicial effect. If the court allows the proponent to disclose those facts or data the court must, upon timely request, restrict the evidence to its proper scope and instruct the jury accordingly.
Comment to 2015 Restyling: All references to an “inference” have been deleted because this makes the Rule flow better and easier to read, and because any “inference” is covered by the broader term “opinion.” Courts have not made substantive decisions on the basis of any distinction between an opinion and an inference. No change in current practice is intended.