706.3Basis of Opinion [Rule 703]

Last Updated: 12/01/23

Key Concepts

  • An expert witness’s opinion may be based on (i) personal knowledge, (ii) facts and data presented at the hearing, or (iii) facts and data gathered outside of court, if they are of a type reasonably relied upon by experts in that field.
  • As long as the facts and data the expert uses to form an opinion are of a type reasonably relied upon by experts in the field, the facts and data do not have to be admissible as evidence.

The Basic Rule

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 him 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.

G.S. 8C-703.

Legal Overview

There are three possible sources for the facts and data upon which an expert may base his or her opinion:

(i) personal observation;

(ii) presentation at trial through a hypothetical question or by having the expert attend the trial to hear testimony and render an opinion; or

(iii) presentation of data to the expert outside of court.

G.S. 8C-703, Official Commentary. See, e.g., State v. Jones, 54 N.C. App. 482 (1981) (expert medical opinion was properly based on both personal knowledge from an examination of the patient as well as data obtained outside of court through lab tests and review of hospital records).

As long as the facts or data underlying the expert’s opinion are “of a type reasonably relied upon by experts in the particular field,” the facts and data do not have to be independently admissible. G.S. 8C-703; State v. Allen, 322 N.C. 176 (1988); State v. Wade, 296 N.C. 454 (1978). Therefore, inadmissible evidence (such as hearsay) may be used by the expert to form his or her opinion as long it is the type of evidence reasonably relied on by such experts. See, e.g., State v. Daughtry, 340 N.C. 488 (1995); State v. Bunn, 173 N.C. App. 729 (2005); State v. Richardson, 112 N.C. App. 58 (1993).

Practice Pointer

What about Crawford and confrontation?
An expert witness may base his or her opinion on facts or data that are not admissible at trial without violating a defendant’s Sixth Amendment right to confront the witnesses against him. The confrontation clause is satisfied because the facts and data are only being used for the purpose of forming the expert’s opinion, and the expert is present in court and subject to cross-examination. See State v. Huffstetler, 312 N.C. 92 (1984), cert denied, 471 U.S. 1009 (1985).
There are, however, significant limitations on the use of substitute experts. While an expert may rely upon data collected by others, he or she may only testify as to his or her independent opinion. If the expert serves as a mouthpiece for another expert’s opinion, the expert’s testimony violates the defendant’s right of confrontation. For more information, see the related Expert Testimony entry on Crawford & Substitute Analysts.

Even though the facts and data forming an expert’s opinion “need not be admissible,” the underlying facts and data may not be offered as substantive evidence unless there is an alternative and proper basis for their admissibility. See State v. Huffstetler, 312 N.C. 92 (1984), cert denied, 471 U.S. 1009 (1985); State v. Bunn, 173 N.C. App. 729 (2005).  
Facts and data “of a type reasonably relied upon” means that the material is commonly used and accepted by experts in that field and generally considered to be reliable. See, e.g., State v. Demery, 113 N.C. App. 58 (1993) (forensic serologist appropriately relied on statistical information about blood group typing since “similar statistics are commonly used and accepted in forensic serology throughout the country”); State v. Teeter, 85 N.C. App. 624 (1987) (psychologist’s expert opinion reasonably relied on interview of victim as well as research and literature that were accepted as reliable in the field); State v. Turner, 66 N.C. App. 203 (1984) (forensic chemist’s opinion about value of drugs and the number of “nickel bags” that could be sold from that quantity was admissible based on his training and experience, and his in-person interviews with users and dealers “about how much marijuana is worth and what it sells for”).

For more information about when and how the basis of an expert witness’s opinion may (or must) be disclosed and the purposes for which the facts and data so disclosed may be used at trial, see the related Evidence entry on Disclosure of Underlying Facts or Data [Rule 705].

Portions of this entry were excerpted from Jessica Smith, “Criminal Evidence: Expert Testimony,” North Carolina Superior Court Judges’ Benchbook, August 2017.