Legal Memorandum: Admissibility of facts forming basis of opinion testimony

Issue: Under the Illinois Rules of Evidence, must the facts an expert refers to when forming his or her opinion be admissible as evidence?

Illinois Rule 703 discusses the admissibility of facts or data which form the basis of opinion testimony by experts.

Rule 703.  Bases of Opinion Testimony by Experts

The facts or data in the particular case upon which an expert bases an opinion or inference may be those perceived by or made known to the expert at or before the hearing. If of a type reasonably relied upon by experts in the particular field in forming opinions or inferences upon the subject, the facts or data need not be admissible in evidence.

Ill. R. Evid. 703 (2015).

The use of an ultrasound image from a treatise to show the basis for an expert’s opinion was discussed in Sharbono v. Hilborn:

The use of an exhibit with an ultrasound image from a treatise to show the basis for an expert’s opinion is permissible under Wilson v. Clark, 84 Ill.2d 186, 417 N.E.2d 1322, 49 Ill. Dec. 308 (1981), and Illinois Rule of Evidence 703 . . . , if a proper foundation has been established and if there has been proper disclosure. In this case, however, it was never established that the learned treatise, from which the ultrasound images were taken, was a reliable authority as required. . . . See Wilson, 84 Ill.2d at 192-96 (an expert may testify about facts or data upon which he or she has based his opinion if those facts or data are of […]

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