Third Circuit: Expert Testimony Need Not Reflect A “Reasonable Degree Of Scientific Certainty"


Expert certainty was not required for handwriting expert, as the expert opined that only a few documents were “definitely” authored by the defendant, some were “probably” authored by him and no “definitive conclusion” could be reached on the balance; any questions concerning the degree of certainty went to the weight of the evidence and not admissibility, in United States v. Mornan, 413 F.3d 372 (3d Cir. 2005)

A Third Circuit case reviewing the admissibility of a handwriting expert testimony highlights two interesting expert issues. First, handwriting not specific; Second, notes reasonable certainty is not required under FRE 702. In the case, the defendant was convicted in a telemarketing fraud scheme offering loans to high-risk borrowers. At trial, a forensic document examiner testified as a handwriting expert whether “a signature on a lease, some handwritten notes, and signatures on money orders were authored by Mornan.” Mornan, 413 F.3d at 376.

Out of 21 pages which she reviewed, the expert opined that the defendant “definitely” authored four documents, “probably” wrote two documents, and was unable to reach “a definitive conclusion” on 15 documents, “testifying that she was only able to note similarities between these documents and Mornan’s handwriting, but not enough to conclude that he was definitely, or even probably, the author.” Id. During cross-examination, the expert was asked whether her opinions were provided “within a reasonable degree of scientific certainty.” The expert replied, “I think they are.” Id. The defendant was convicted and appealed the admission of the handwriting expert testimony.

The circuit affirmed the admission of the handwriting expert testimony. Because the defendant did not object to the expert testimony or the expert’s qualifications, the matter was reviewed for plain error. On the cross-examination concerning a “reasonable degree of scientific certainty,” the circuit noted:

“As the Government has pointed out, however, there is nothing magical about the phrase, `to a reasonable degree of scientific certainty.' It is not derived from the language of Rule 702 itself, and this Court has been unable to find any authority to support the position that questions regarding the expert's ‘degree of scientific certainty’ categorically renders expert testimony inadmissible.” Id. at 381 (citation to government brief omitted).
The circuit noted that handwriting comparison was subject to a continuum of “probabilities rather than certainties,” and certainty was not required for this field. Any issues concerning the certainty of the opinion went to its weight and not its admissibility.

Consequently, there was no error (or even plain error) in admitting the expert’s handwriting analysis testimony.

The issue of expert certainty was recently noted in a prior post. See FRE 702 Does Not Require That Medical Expert Testimony Be Based On “A Reasonable Medical Certainty”. For another post on handwriting expert testimony, see Handwriting Expert Testimony Satisfied Five Daubert Reliability Factors.

Federal Rules of Evidence