Whether expert testimony that an alleged child victim's inconsistent reporting of abuse is consistent with truthfulness is admissible under Federal Rule of Evidence 702(a)

QUESTION PRESENTED Federal Rule of Evidence 702(a) permits expert witness testimony only where the expert’s “knowledge will help the trier of fact understand the evidence or to determine a fact in issue.” Most courts hold testimony that vouches for a witness’s credibility is not admissible under Rule 702 because it invades the jury’s exclusive role to make credibility determinations. Some courts even hold that testimony which only implicitly touches credibility is properly excluded because it inevitably would encroach on the jury’s role. In United States v. Salerno, 506 U.S. 317, 312-22 (1992), this Court explained that courts “cannot alter evidentiary rules merely because litigants might prefer different rules in a particular set of cases.” And in United States v. Tome, 513 U.S. 150, 166 (1995), this Court acknowledged the difficulties inherent in prosecuting cases involving child victims, but it reiterated the Salerno holding that evidentiary rules cannot be relaxed to make prosecution easier. The question presented is: In a prosecution for aggravated child sexual abuse in which the alleged victim has inconsistently reported abuses, may the prosecution present expert testimony that such behavior is consistent with the alleged victim telling the truth, even though similar testimony is excluded when it would favor defendants because it “inevitably would encroach upon” the jury’s exclusive role to determine the credibility of witnesses?