See also: BATTERED WOMAN SYNDROME; CHARACTER
CHILD SEXUAL ABUSE ACCOMODATION SYNDROME; EYEWITNESS TESTIMONY
IMPEACHMENT ; RAPE TRAUMA SYNDROME
SEXUAL ABUSE ACCOMODATION SYNDROME; TRUTHFULNESS
WITNESSES.

1.  Generally

The term “credibility” as used in this article means the degree to which  the substance of a document or a witness’ testimony ought to inspire belief in the matter asserted, based on all of the surrounding cirumstances, including other evidence in the case.{footnote}See also Webster’s Ninth New Collegiate Dictionary 305 (1990) (“1: the quiality or power of inspiring belief”).{/footnote}   “Truthfulness,” on the other hand, refers to a witness’ general propensity to lie or tell the truth, and is simply one of the factors that may be considered in judging the credibility of a witness’ testimony. Thus, a psychiatrist’s testimony that a child is probably telling the truth in court about past instances of sexual abuse is testifying about the credibility of the child’s testimony; a psychiatrist who testifies that a witness is a pathological liar is opining on the witness’ character trait for truthfulness. See TRUTHFULNESS.

Evidence may not be excluded by the court in a jury trial simply because the court does not find it to be credible: determinations of credibility are for the jury, not the judge.{footnote}Bowden v. McKenna, 600 F.2d 282, 284-85 (1st Cir.), cert.   denied, 444 U.S. 899 (1979); Ballou v. Henri Studios, Inc., 656 F.2d 1147, 1154 (5th Cir. 1981); United States v. Thompson, 615 F.2d 329, 332 (5th Cir. 1980); Western Industries, Inc. v. Newcor Canada Ltd., 739 F.2d 1198, 1202 (7th Cir. 1984).
Wright & Graham, Federal Practice and Procedure: Evidence § 5214 at 265-66 ("In the first place, credibility is a question for the jury; to permit the judge to exclude evidence on the ground that he thinks it incredible would be a remarkable innovation and may even be a violation of the right of trial by jury.") {/footnote}

2.  Opinion as to a Witness’ Credibility

Opinion testimony as to a witness’ credibility is governed by FRE 608(a), which provides:

Opinion and reputation evidence of character.  The credibility of a witness may be attacked or supported by evidence in the form of opinion or reputation, but subject to these limitations: (1) the evidence may refer only to character for truthfulness or untruthfulness, and (2) evidence of truthful character is admissible only after the character of the witness for truthfulness has been attacked by opinion or reputation evidence or otherwise.

This rule has been held to bar witnesses from expressing any opinion of another witness’ credibility other than an opinion about a witness’s character for truthfulness.{footnote}United States v. Awkard, 597 F.2d 667, 670 (9th Cir.) ("under the Federal Rules, opinion testimony on credibility is limited to character; all other opinions on credibility are for the jurors themselves to form."), cert. denied, 444 U.S. 885 (1979); United States v. Cox, 23 M.J. 808 (N.M.C.C.M.R. 1986).
See also United States v. Price, 722 F.2d 88, 90 (5th Cir. 1983) (admission of Revenue Agent’s testimony that he relied on statements of two people in his investigation because he "believed them" constituted reversible error), cert. denied, 473 U.S. 904 (1985).
See also State v. Middleton, 657 P.2d 1215, 1221 (Ore. 1983) ("a witness, expert or otherwise, may not give an opinion on whether he believes a witness is telling the truth.”)
Contra Margaret A. Berger, The Second Circuit Review — 1987-1988 Term: Evidence: United States v. Scop: The Common-Law Approach To An Expert’s Opinion About A Witness’s Credibility Still Does Not Work, 55 Brooklyn L. Rev. 559 (1989).
{/footnote}

Expert testimony is generally not allowed on the issue of a witness’ credibility.{footnote}United States v. Cecil, 836 F.2d 1431, 1441-42 (4th Cir.), cert. denied, 487 U.S. 1205 (1988) ("a psychiatrist may not testify to the credibility of a witness; that issue is for the jury"); United States v. Benson, 941 F.2d 598, 604 (7th Cir. 1991); United States v. Affleck, 776 F.2d 1451, 1458 (10th Cir. 1985) (The trial court in a securities fraud case properly excluded expert testimony about the defendant’s memory on the ground that an untrained layman could intelligently evaluate the evidence without expert assistance.); United States v. Samara, 643 F.2d 701, 705 (10th Cir. 1981).
See generally Annotation, Necessity and Admissibility of Expert Testimony as to  Credibility  of Witnesses,  20 A.L.R.3d 684 (1968).
See also BATTERED WOMAN SYNDROME; CHILD SEXUAL ABUSE ACCOMODATION SYNDROME; RAPE TRAUMA SYNDROME; SEXUAL ABUSE ACCOMODATION SYNDROME.{/footnote} This rule has been justified by the argument that issues of credibility are reserved for the jury to determine,{footnote}United States v. Cecil, 836 F.2d 1431, 1441-42 (4th Cir.), cert. denied, 487 U.S. 1205 (1988).{/footnote} the trier of fact is capable of judging credibility without expert assistance,{footnote}United States v. Benson, 941 F.2d 598, 604 (7th Cir. 1991); United States v. Affleck, 776 F.2d 1451, 1458 (10th Cir. 1985).
State v. Castro, 756 P.2d 1033, 1044 (Haw. 1988) (psychologist erroneously permitted to give opinion on the credibility of adult assault victim); People v. Cox, 557 N.E.2d 288  (Ill. Ct. App. 1990) (rape victim’s treating physician erroneously permitted to testify that he remembered treating the victim because, “A person who comes in distraught, upset, certainly arouses more apparent validity for the claim . . . ."; such matters held to be within the range of understanding and knowledge of the average person).
CHECK State v. Saldana, 324 N.W.2d 227, 231 (Minn. 1982).
CHECK Johnson v. State, 438 So. 2d 774 (Fla. 1983), cert. denied, 465 U.S. 1051 (1984); Commonwealth v. Francis, 390 Mass. 89, 453 N.E.2d 1204 (1983).
CHECK United States v. Ellsworth, 738 F.2d 333 (8th Cir. 1984), United States v. Ramirez, 871 F.2d 582, 585 (6th Cir. 1989) (allowing each side to present experts regarding a witness’ credibility would raise even more issues for the jury); Garner v. Santoro, 865 F.2d 629, 645 (5th Cir. 1989) ("Thus, we have a ‘battle of the experts,’ and the jury ‘must be allowed to make credibility determinations and weigh the conflicting evidence in order to decide the likely truth of a matter not itself initially resolvable by common knowledge or lay reasoning.’") (quoting Osburn v. Anchor Labs., 825 F.2d 809 (5th Cir. 1987), cert. denied, 108 S. ct. 1476 (1988)).{/footnote} allowing such testimony may unduly influence the jury,{footnote}United States v. Benson, 941 F.2d 598, 604 (7th Cir. 1991).{/footnote} and the prejudicial effect outweighs the probative value.{footnote}State v. Stucke, 419 So. 2d 939, 945 (La. 1982) (The prejudicial effect of expert testimony on witness credibility outweighs its probative value and usurps the jury function.)
{/footnote} 

Some courts have held that the admissibility of such testimony is a matter within the trial court’s discretion.{footnote}United States v. Pacelli, 521 F.2d 135, 140 (2d Cir. 1975); United States v. Rohrer, 708 F.2d 429, 434 (9th Cir. 1983); United States v. Sessa, 806 F. Supp. 1063, 1069 (E.D.N.Y. 1992) (Weinstein, J.) (“psychologist’s opinion on a witness’s credibility can be useful to a jury under Rule 702 in some circumstances but not in others.”; excluding opinion as unhelpful under the circumstances).
{/footnote} The rule has also been relaxed with respect to child witnesses in abuse cases.  See CHILDREN 3.  Expert Testimony.

Bibliography

Steven I. Friedland, On Common Sense And The Evaluation Of Witness Credibility, 40 Case W. Res. 165 (1990).
Ingulli, Trial By Jury: Reflections On Witness Credibility, Expert Testimony, and Recantation, 20 Val. U.L. Rev. 145 (1986).