Disclosing the Facts or Data Underlying an Expert’s

Opinion Unless the court orders otherwise, an expert may state an opin- ion—and give the reasons for it—without first testifying to the underlying facts or data. But the expert may be required to dis- close those facts or data on cross-examination. (As amended Mar. 2, 1987, eff. Oct. 1, 1987; Apr. 22, 1993, eff. Dec. 1, 1993; Apr. 26, 2011, eff. Dec. 1, 2011.)