concurring in the result:
My colleagues ultimately conclude that the trial court’s exclusion of appellant’s proffered expert testimony on eyewitness identification was harmless in view of the strong corroborative evidence of appellant’s guilt. I do not take issue with that conclusion. However, in what could be viewed as extended dicta, my colleagues assert it was not error for the trial court to exclude the expert testimony based on the anticipated strength of the government’s evidence, rather than on the particularized inquiry required by our decisions in Dyas v. United States1 and Benn v. United States (Benn II).2 I write separately to express my disagreement with that assertion. In my view, fundamental principles of the law of evidence make it clear that the strength of the government’s evidence of appellant’s guilt was not a proper factor for the trial court to consider. Moreover, a rule of evidence allowing the trial court to exclude a criminal defendant’s expert witness because of the perceived strength of the prosecution’s evidence would be unconstitutional, for it would constitute an arbitrary infringement on the defendant’s right to a meaningful opportunity to present a complete defense.
Appellant’s defense at trial was misiden-tification — he claimed that Ms. Kuczynska was mistaken in identifying him as the unknown person who robbed her at gunpoint. In support of that claim, appellant called Monica Barnes to the witness stand. She testified that it was Jarwon Scott, not appellant, who gave her Ms. Kuezynska’s cell phone and checkbook after the robbery. In further support of his misidenti-fication defense, appellant sought to call Dr. Henry Shulman, a psychologist. According to appellant’s proffer, Dr. Shulman could have testified as an expert on factors present in this case that had been shown in controlled scientific experiments to reduce the accuracy of eyewitness identifications of strangers. These factors included the cross-racial nature of the identification,3 the brevity of Ms. Kuezynska’s interaction with her assailant, and the stress and emotional arousal she experienced during the armed robbery. Dr. Shulman would have identified and discussed these factors and the science behind them without offering any opinion of his own on the ultimate question of whether Ms. Kuezyns-ka’s identification of appellant was reliable. Appellant argued that the information provided by Dr. Shulman would assist the jury in deciding for itself how much weight to give Ms. Kuezynska’s identification testimony.
Prior to the start of appellant’s first trial, the trial judge excluded Dr. Shul-man’s testimony. In other cases, the judge acknowledged, he had found Dr. Shulman’s expert testimony on cross-racial identifications to be helpful to the jury and admitted it.4 But as the judge explained, *246there was little evidence corroborating the identifications in those cases. The judge understood appellant’s case to be different, in that the government expected to present “abundant corroborative evidence” of Ms. Kuczynska’s identification of appellant. Relying on the government’s proffer, the judge cited appellant’s attempt to pass one of Ms. Kuczynska’s stolen checks, the discovery of the robbery proceeds in a motel room associated with appellant, and his presence in a vehicle linked to the charged robberies. Given such corroboration, the judge concluded, Dr. Shulman’s expert testimony “would [not] be of any assistance to the trier of fact” in assessing the reliability of Ms. Kuczynska’s identification. Rather, the judge stated, “on these facts” the jury would likely “give undue weight to [Dr. Shulman’s] opinion in the narrow area of cross-racial identification,” and the probative value of the testimony would be outweighed by the danger of unfair prejudice.
The logic of the judge’s ruling is not entirely clear. It appears the judge reasoned that if Ms. Kuczynska’s identification of appellant was corroborated by the proffered circumstantial evidence of appellant’s guilt, a sensible jury could not find the identification unreliable for the reasons Dr. Shulman would have identified. But it is difficult to see how that conclusion follows, inasmuch as the corroborative evidence did not invalidate Dr. Shulman’s proffered testimony or render it irrelevant to the facts of this case. The corroborative evidence certainly was not conclusive, and the judge could not know whether the defense would succeed in weakening it at trial, or what weight the jury would give to it. It is equally difficult to understand the judge’s conclusion that because the circumstantial evidence corroborated Ms. Kuc-zynska’s identification, the probative value of the expert testimony would be outweighed by the danger of unfair prejudice. As used in this context, the term “unfair prejudice” is understood to “meant ] an undue tendency to suggest decision on an improper basis, commonly, though not necessarily, an emotional one.”5 No such danger was identified in this case. Nor did the judge explain why he feared the jury would give “undue weight” to Dr. Shulman’s testimony. It is the jury’s prerogative to weigh the admissible evidence as it sees fit. (If anything, though, one would think the impact of defense evidence would be greatest when the government’s case is weak, not when it is strong.) In sum, from all appearances, the judge prejudged the strength of the prosecution’s evidence and excluded the defense expert only because he believed the government’s evidence in toto would be too powerful for the expert testimony by itself to rebut.
Whatever the judge’s precise rationale, I think he exercised his discretion erroneously in relying on the fact that Ms. Kuc-zynska’s identification was corroborated by circumstantial evidence to exclude Dr. Shulman’s testimony. The ruling runs counter to basic principles of the law of evidence. The judge did not find, nor could he have found, that Dr. Shulman’s testimony was irrelevant. In general, if evidence is relevant, it should be admitted unless it is barred by some other legal *247rule.6 “There are two components to relevant evidence: materiality and probative value.”7 “[T]he fact sought to be established by the evidence must be material, which is to say that the party must establish that fact as a condition to prevailing on the merits of his case.”8 And the evidence must have probative value, meaning “the tendency of evidence to establish the proposition that it is offered to prove.”9 The probativity threshold for purposes of admissibility is low: An item of evidence, to be relevant, need only “tend[ ] to make the existence or nonexistence of a fact more or less probable than would be the case without that evidence.”10 As Professor McCormick explains:
An item of evidence, being but a single link in the chain of proof, need not prove conclusively the proposition for which it is offered. It need not even make that proposition appear more probable than not. Whether the entire body of one party’s evidence is sufficient to go to the jury is one question. Whether a particular item of evidence is relevant to the case is quite another. It is enough if the item could reasonably show that a fact is slightly more probable than it would appear without that evidence. Even after the probative force of the evidence is spent, the proposition for which it is offered still can seem quite improbable! 11
“Ordinarily,” therefore, “any evidence which is logically probative of some fact in issue is admissible[,] and if the evidence offered conduces in any reasonable degree to establish the probability or improbability of a fact in controversy, it should go to the jury.” 12 Thus, evidence may not be rejected as irrelevant merely because it is contradicted by other evidence. “This is an inappropriate basis to exclude evidence, *248because it preempts the jury’s role as fact-finder.” 13
Furthermore, this Court has recognized that “[probative evidence should not be excluded because of ‘crabbed notions of relevance or excessive mistrust of juries,’ ”14 and we have embraced “the policy of admitting as much relevant evidence as it is reasonable and fair to include.”15 Accordingly, we have chosen to follow the federal rule that relevant and otherwise admissible evidence may be excluded only “if its probative value is substantially outweighed by a danger of one or more of the following: unfair prejudice, confusing the issues, misleading the jury, undue delay, wasting time, or needlessly presenting cumulative evidence.”16
I see no reason why the foregoing principles should not apply with equal force to the admission of relevant expert testimony. The standard of relevance is the same for expert testimony as it is for other evidence; as we have held, “there is only one standard of relevance.”17 And in Benn II we endorsed the principle that “judges should rely on the adversary system, rather than on the exclusion of evidence, to guard against potential juror confusion from the presentation of scientific evidence.”18 We added that “[a]ny remaining concern a trial judge may have that admission of expert testimony could confuse or overwhelm the jury is more appropriately dealt with, not by exclusion, but by placing reasonable limitations on the expert’s testimony and instructing the jurors that they — and only they — are the ultimate fact finders.”19
It is true that “[i]n a jury trial the judge must exercise discretion to decide whether the proffered expert testimony is likely to assist the jury in the performance of its duties — that is to say, in understanding the evidence, determining the facts that must be found and rendering its verdict.” 20 But such helpfulness to the jury is determined by the three criteria governing the admissibility of expert opinion testimony set forth in Dyas,21 and ultimately turns on “the relevance and probative val*249ue of the proposed scientific evidence.”22 This seems to me to mean that the criterion of helpfulness is met if the expert testimony is relevant and if its probative value is not substantially outweighed by the danger of unfair prejudice or other legitimate concerns. It would be anomalous to interpret the criterion of helpfulness to allow the judge to exclude relevant and otherwise admissible expert testimony merely because the judge is convinced by the strength of the opposing party’s evidence and therefore believes the expert’s testimony is unconvincing. Such concerns go to the weight of the expert testimony, which is “exclusively for the jury” to determine,23 not to its admissibility. As Judge Posner has explained (addressing a trial judge’s erroneous exclusion of expert opinion testimony), “a judge in our system does not have the right to prevent evidence from getting to the jury merely because he does not think it deserves to be given much weight. He may comment to the jury on the weight of the evidence (though few federal judges do that nowadays), and he may have to balance weight against prejudice in ruling on objections under Fed.R.Evid. 403, but he may not screen witnesses simply to decide whether their testimony is persuasive.”24
In taking the opposing view, my colleagues rely on cases in which we have said that where corroboration of a challenged identification exists, the exclusion of proffered expert testimony on eyewitness identification generally does not constitute an abuse of discretion.25 But that does not mean the existence of corroboration is a legitimate reason for the trial court to exclude the expert testimony; it only means that the exclusion likely will not be so prejudicial as to necessitate reversal by the appellate court. Abuse of discretion is a standard of appellate review incorporating an assessment of prejudice. A trial court exercises its discretion erroneously when it relies on an improper factor,26 but “the reviewing court must weigh the severity of the error against the importance of the determination in the whole proceeding and the possibility for prejudice as a result.”27 It is only when the impact of the error is so serious we must reverse that we say the trial court “abused” its discretion.28 I readily grant that where a challenged identification is corroborated, the appellate court may be able to conclude that the erroneous exclusion of expert testimony on eyewitness identification was harmless, and hence that there was no “abuse” of discretion. That is what we conclude in this case.29 But to *250say the trial court did not abuse its discretion is not to say the court exercised its discretion properly.30
Furthermore, at least in criminal cases, a rule of evidence permitting the trial judge to bar a defendant from introducing relevant and otherwise admissible expert testimony merely because the judge perceives the prosecution’s proffered opposing evidence to be strong would raise a serious constitutional question. As the Supreme Court made clear in Holmes v. South Carolina,31 such a rule likely would violate the defendant’s constitutional right to a meaningful opportunity to present a complete defense.
Holmes considered a South Carolina rule of evidence under which the defendant was barred from introducing proof of third-party guilt if the prosecution had forensic evidence (e.g., DNA testing) that, if believed, strongly proved the defendant’s guilt. Under this rule, the Supreme Court noted, the trial judge did not “focus on the probative value or the potential adverse effects of admitting the defense evidence,” and did not assess the strength of the prosecution’s evidence in light of the defendant’s challenges to its reliability.32
With those features, the Court found, the South Carolina evidentiary rule was an arbitrary infringement on the defendant’s right to have a meaningful opportunity to present a complete defense. As the Court explained:
Just because the prosecution’s evidence, if credited, would provide strong support for a guilty verdict, it does not follow that evidence of third-party guilt has only a weak logical connection to the central issues in the case. And where the credibility of the prosecution’s witnesses or the reliability of the evidence is not conceded, the strength of the prosecution’s case cannot be assessed without making the sort of factual findings that have traditionally been reserved for the trier of fact and that the South Carolina courts did not purport to make in this case.
The rule applied in this case is no more logical than its converse would be, ie., a rule barring the prosecution from introducing evidence of a defendant’s guilt if the defendant is able to proffer, at a pretrial hearing, evidence that, if believed, strongly supports a verdict of not guilty....
The point is that, by evaluating the strength of only one party’s evidence, no logical conclusion can be reached regarding the strength of contrary evidence offered by the other side to rebut or cast doubt.[33]
As is demonstrated in the present case, a rule allowing the trial judge to exclude the defendant’s expert testimony on eye*251witness identification if the prosecution proffers strong corroboration of the defendant’s guilt is analogous to, and suffers from the same fatal flaws as, the South Carolina rule held unconstitutional in Holmes. The judge in this case did not appraise the probative value or potential adverse effects of Dr. Shulman’s testimony, nor did he assess the prosecution’s evidence in light of the defendant’s challenges to its reliability. By evaluating only the prosecution’s proffered evidence, the judge could reach no logical conclusion regarding the strength of the expert testimony offered by appellant to rebut or cast doubt on the government’s case. And if the judge had attempted to weigh all the evidence in order to determine the question of admissibility, he would have exceeded his mandate and invaded the role of the jury as trier of fact.
Thus, I think the trial judge in the present case erred in concluding that the existence of circumstantial evidence corroborating Ms. Kuczynska’s identification of appellant justified excluding Dr. Shulman’s expert testimony. As proffered, that testimony would have been relevant, i.e., material and probative, because it would have tended to make Ms. Kuczynska’s identification of appellant less probable.34 The proffer sufficed to oblige the judge to conduct a particularized inquiry and evaluate the expert testimony under the criteria for admissibility set forth in Dyas.35 Without a proper inquiry, as we explained in Benn II, it was error to reject any of the proffered testimony as unnecessary.36
. 376 A.2d 827, 832 (D.C.1977).
. 978 A.2d 1257, 1269-70, 1273-74 (D.C.2009).
. According to appellant’s proffer, Dr. Shul-man would have testified that "[ejyewitnesses are less likely to be accurate in identifying people of a different ethnicity than they are in identifying people of their own ethnicity.”
.The judge considered the rest of Dr. Shul-man’s proffered expert testimony unnecessary, believing that the standard jury instruc*246tion on identification provides the jury "with all the guidance it needs to be able to determine the accuracy and reliability of eyewitness identification.” As discussed below, this categorical rejection of the expert testimony is at odds with our subsequent decision in Benn II.
. Mercer v. United States, 724 A.2d 1176, 1184 (D.C.1999) (internal quotation marks omitted).
. See, e.g., Reavis v. United States, 395 A.2d 75, 78 (D.C. 1978) ("Relevance, and the concepts it embodies, determines initially whether a proffered item of evidence will be admissible.”); 2 Clifford S. Fishman, Jones on Evidence § 11:1 at 258 (7th ed. 2000) ("Evidence that is relevant should be admitted, unless barred by some other rule.”); 1 Kenneth S. Broun et al„ McCormick on Evidence § 184 at 728 (6th ed. 2006) ("[Ujnless there is some such distinct ground for refusing to hear the evidence, it should be received.”) (footnote omitted); Fed.R.Evid. 402 ("Relevant evidence is admissible unless any of the following provides otherwise: the United States Constitution; a federal statute; these rules; or other rules prescribed by the Supreme Court. Evidence which is not relevant is not admissible.”).
. McCormick on Evidence § 185 at 729 (footnote omitted).
. Reavis, 395 A.2d at 78; see also McCormick on Evidence § 185 at 729 ("[Materiality] looks to the relation between the propositions that the evidence is offered to prove and the issues in the case.”).
. Id. § 185 at 730.
. Punch v. United States, 377 A.2d 1353, 1358 (D.C.1977); accord Plummer v. United States, 813 A.2d 182, 188 (D.C.2002) ("Evidence is relevant if it has ‘any tendency to make the existence of any fact that is of consequence to the determination of the action more probable or less probable than it would be without the evidence.' ”) (quoting Street v. United States, 602 A.2d 141, 143 (D.C.1992)); Fed.R.Evid. 401 ("Evidence is relevant if: (a) it has any tendency to make a fact more or less probable than it would be without the evidence; and (b) the fact is of consequence in determining the action.”).
. McCormick on Evidence § 185 at 733 (footnotes omitted). See, e.g., Winfield v. United States, 676 A.2d 1, 4 (D.C.1996) (en banc) (holding that when the defendant seeks to introduce evidence of a third-party perpetrator, "there is no requirement that the proffered evidence must prove or even raise a strong probability that someone other than the defendant committed the offense”) (internal quotation marks and alterations omitted).
. Plummer, 813 A.2d at 188-89 (internal quotation marks and brackets omitted).
. Jones on Evidence § 11:8 at 281-82 (footnote omitted). Evidence is irrelevant in the sense that it lacks probative value only if "the evidence does not justify any reasonable inference as to the fact in question. Cases involving such evidence are few and far between.” McCormick on Evidence § 185 at 735 (emphasis in original; footnote omitted).
. Allen v. United States, 603 A.2d 1219, 1224 (D.C.1992) (en banc) (quoting Riordan v. Kempiners, 831 F.2d 690, 698 (7th Cir.1987)).
. (William A.) Johnson v. United States, 683 A.2d 1087, 1100 (D.C.1996) (enbanc).
. Fed.R.Evid 403 (emphasis added); see (William A.) Johnson, 683 A.2d at 1099 ("The 'substantially outweighs’ approach is apparently the product of the general federal policy promoting the admission of as much relevant evidence as reasonably possible.”).
. Winfield, 676 A.2d at 3.
. Benn II, 978 A.2d at 1275.
. Id.
. Hager v. United States, 856 A.2d 1143, 1147 (D.C.2004) (quoting Steele v. D.C. Tiger Market, 854 A.2d 175, 181 (D.C.2004)) (internal quotation marks omitted), amended by 861 A.2d 601 (D.C.2004).
. The three criteria of admissibility set forth in Dyas that a judge must consider are: (1) whether the subject matter of the testimony is "beyond the ken of the average layman”; (2) whether the witness is sufficiently qualified as to make it appear that her expertise will "probably aid” the trier of fact; and (3) whether the state of the pertinent art or scientific knowledge permits a reasonable opinion to be asserted. 376 A.2d at 832. My colleagues concede that "the Dyas test does not include corroboration.” Ante at 238.
. Benn II, 978 A.2d at 1278.
. Jenkins v. United States, 113 U.S.App.D.C. 300, 309, 307 F.2d 637, 646 (1962).
. Western Indus., Inc. v. Newcor Can., Ltd., 739 F.2d 1198, 1202 (7th Cir.1984) (internal citation omitted). Thus, I believe my colleagues are quite mistaken in giving trial judges a green light to reject relevant expert testimony as unhelpful based on their own "[ljife experiences.” Ante at 238 (“Life experiences are sufficient and a trial judge must be vested with discretion to sort out the various situations where experts may illuminate the question.”). Such carte blanche invites subjective adjudication in the guise of "discretion” and disregards fundamental principles of our jurisprudence limiting the role of judges in jury trials, not to mention the teachings of Benn II, Dyas, and myriad other cases, concerning the standards for determining the admissibility of expert testimony.
. Ante at 237-38 n. 13 (citing Benn II, 978 A.2d at 1280, and Hager, 856 A.2d at 1149).
. (James W.) Johnson v. United States, 398 A.2d 354, 365 (D.C.1979).
. Id. at 367.
. Id.
. See also Heath v. United States, 26 A.3d 266, 282-85 (D.C.2011) (holding erroneous exclusion of expert testimony to have been harmless).
.My colleagues also assert that the corroborative evidence "hardly left the verity of [Ms. Kuczynska’s] identification of appellant as the actual robber beyond the ken of the jury.” Ante at 239. But this is a non sequitur. The fact that the identification was corroborated is irrelevant to the pertinent question, which is whether the scientific subject matter of Dr. Shulman’s testimony was beyond the ken of the average layperson (the first Dyas criterion). On that question, the trial judge made no inquiry or ruling. However, as we explained in Bern II, even though "jurors may be familiar from their own experience with factors relevant to the reliability of eyewitness observation and identification, ... it cannot be said that psychological studies regarding the accuracy of an identification are within the ken of the typical juror.” 978 A.2d at 1277 (internal quotation marks omitted).
. 547 U.S. 319, 126 S.Ct. 1727, 164 L.Ed.2d 503 (2006).
. Id. at 329, 126 S.Ct. 1727.
. Id. at 330-31, 126 S.Ct. 1727.
.This is not a case where testimony regarding the reliability of stranger identifications would have been beside the point because the victim knew the perpetrator she identified or because her identification was not in dispute. Cf. Heath, 26 A.3d at 282 ("[T]his expert testimony would have been of scant relevance to the identifications of appellant by Ms. Ervin and Ms. Carter, whatever the reliability of those identifications,, because they already knew appellant at the time of the shooting.”); Hager v. United States, 856 A.2d 1143, 1148-49 (D.C.2004) (expert testimony unhelpful where the "studies on which [the expert] would have relied concern[ed] the reliability of a stranger identification, not an identifica-don of a person known to the witness, as in this case”).
. See footnote 21, supra.
. See Benn II, 978 A.2d at 1275 ("[E]ven if the trial court did not apply an automatic rule of exclusion, the ruling was nonetheless defective because it did not address the correct legal factors set out in Dyas or apply them to the expert testimony that the defense proffered.”); see also id. at 1278. Thus, the judge also erred in ruling (see footnote 4, supra) that the standard jury instruction on identification obviated the need for much of Dr. Shulman’s testimony.