dissenting. The trial court in the present case refused to permit the jurors to consider expert testimony that was necessary in order to enable them to evaluate the sole defense that the defendant had raised. In my view, this ruling constituted an abuse of discretion for two reasons: (1) it contradicted a recent opinion rendered by this court and (2) it violated the defendant’s fundamental right under the federal constitution to present a defense. I would reverse the defendant’s conviction and order a new trial.
In the present case, the defendant, Maurice Billie, was charged with committing a number of serious crimes.1 His sole defense was that he had been unable *183to form the requisite mens rea because he was, at all relevant times, under the influence of a substance known as “illy,” which is a mixture of phencyclidine (PCP), wood alcohol, methanol and formaldehyde. In order to establish this defense, the defendant wished to rely upon the expert testimony of Jeremy August, a psychiatrist. August would have testified to the behavioral effects of each of the constituent ingredients of illy. He also would have testified that it was not possible to assess the precise effect of illy upon the defendant, for the simple reason that it was not possible to determine the precise ratio among the various ingredients contained in the particular mixture of illy that the defendant had ingested. The trial court excluded all of August’s testimony on the ground that it was irrelevant. I agree with the Appellate Court’s conclusion that this ruling constituted an abuse of discretion. State v. Billie, 47 Conn. App. 678, 684, 707 A.2d 324 (1998).
“Expert testimony should be admitted when: (1) the witness has a special skill or knowledge directly applicable to a matter in issue, (2) that skill or knowledge is not common to the average person, and (3) the testimony would be helpful to the court or jury in considering the issues. . . .” (Internal quotation marks omitted.) State v. Correa, 241 Conn. 322, 353-54, 696 A.2d 944 (1997). As the Appellate Court cogently explained, the psychiatric expert in the present case “possessed a special knowledge of illy, not common to the average person,2 and his testimony would have *184aided the jury in considering the issue of intoxication. The relevant issue was whether the defendant was under the influence of illy and whether the intoxication affected his capacity to form a specific intent. Testimony concerning the composition of illy and its effect would have aided the jury in considering those issues.” State v. Billie, supra, 47 Conn. App. 684.
The mantra of the majority opinion is that “the trial court has wide discretion in ruling on the admissibility of expert testimony . . . .” (Internal quotation marks omitted.) This is true. Nevertheless, “[discretion means a legal discretion, to be exercised in conformity with the spirit of the law and in a manner to subserve and not to impede or defeat the ends of substantial justice. In a plain case, this discretion has no office to perform, and its exercise is limited to doubtful cases, where an impartial mind hesitates. . . . State v. Onofrio, 179 Conn. 23, 29, 425 A.2d 560 (1979). Discretion does not mean, as the majority seems to believe, an untrammeled right to do as the trial court wishes. See United States v. Brien, 59 F.3d 274, 277 (1st Cir.), cert. denied, 516 U.S. 953, 116 S. Ct. 401, 133 L. Ed. 2d 320 (1995) (trial court’s discretion is not carte blanche); State v. Chapple, [135 Ariz. 281, 296, 660 P.2d 1208 (1983)] (discretion does not mean that the court is free to reach any conclusion it wishes). If discretion were as unbridled as the majority seems to believe, a criminal defendant would be playing Russian roulette whenever his case was assigned to a judge: justice would depend upon which chambers he happened to draw. This is not justice. Rather, a trial court’s discretion must be based upon a reasoned consideration of the unique circumstances of each particular case.” (Internal quotation marks omitted.) State v. McClendon, 248 Conn. 572, 609-10, 730 A.2d 1107 (1999) (Berdon, J., dissenting). With this analytic framework in mind, I am unable to comprehend *185the majority’s determination that the trial court in the present case did not abuse its discretion.
Just a few years ago, a unanimous panel of this court — which included the author of the majority opinion in the present case — held that the trial court had abused its discretion by “excludfing] the testimony of a defense expert regarding the adverse effects of cocaine on the cognitive abilities of a person who ingests the drug . . . .” State v. Barletta, 238 Conn. 313, 316, 680 A.2d 1284 (1996). The result that my colleagues in the majority have reached in the present case cannot be reconciled with Barletta. In fact, the trial court’s ruling in the present case is more egregious than the ruling that the Barletta court found to be an abuse of discretion.
To begin with, the expert testimony in Barletta was highly speculative.3 In the present case, the only uncertainty pertained to the ratio among the ingredients contained in the mixture of illy that the defendant had ingested. It is apparent that August could have informed the jury about the following two matters: (1) the behavioral effects of the individual drugs that compose illy; and (2) the range of possible reactions to differing batches of illy.4 Significantly, the Barletta court was *186untroubled by the state’s argument that “cocaine affects people differently, [and the expert] could not testify with specificity how [the eyewitness’] cognitive abilities were likely to have been impaired . . . Id., 319. If that argument did not suffice to insulate the trial court’s ruling in Barletta, it cannot do so in the present case.5
Moreover, Barletta involved expert psychiatric testimony that was offered in order to impeach the credibility of a witness to a crime. Id., 318. In the present case, August would have testified to the defendant’s state of mind. If the jurors had been permitted to consider August’s testimony, they well may have reached the following conclusions: (1) the defendant did not possess the requisite mens rea; (2) the state had failed to establish a necessary element; and (3) the state had failed to prove the defendant’s guilt beyond a reasonable doubt.6
*187Finally, the majority today has disregarded the defendant’s fundamental right under the sixth amendment to the federal constitution to present a defense. “In order to comport with the constitutional standards embodied in the confrontation clause, the trial court must allow a defendant to expose to the jury facts from which [the] jurors, as the sole triers of fact and credibility, could appropriately draw inferences relating to the reliability of the witness. Davis v. Alaska, [415 U.S. 308, 318, 94 S. Ct. 1105, 39 L. Ed. 2d 347 (1974)]. . . . State v. Beliveau, 237 Conn. 576, 585, 678 A.2d 924 (1996); State v. Barnes, 232 Conn. 740, 746, 657 A.2d 611 (1995). Thus, [w]hen defense evidence is excluded, such exclusion may give rise to a claim of denial of the right to present a defense. Chambers v. Mississippi, [410 U.S. 284, 289-90, 93 S. Ct. 1038, 35 L. Ed. 2d 297 (1973)]. State v. Christiano, 228 Conn. 456, 474, 637 A.2d 382, cert. denied, 513 U.S. 821, 111 S. Ct. 83, 130 L. Ed. 2d 36 (1994); see also State v. Cavell, 235 Conn. 711, 720, 670 A.2d 261 (1996) (under particular circumstances, the unjustified exclusion of a witness’ testimony can amount to a deprivation of the defendant’s right to present a defense).” (Internal quotation marks omitted.) State v. Barletta, supra, 238 Conn. 322. In the present case, the defendant’s sole defense was that he was unable to form the requisite mens rea. By excluding the testimony of the psychiatric expert witness, the court deprived the defendant of the only credible means by which he could explain this defense to the jury.7 Without the benefit of this testimony, the jury was unable to evaluate the case mounted by the defense in an informed manner. For these reasons, the trial court’s *188ruling deprived the defendant of his fundamental right under the constitution to present a defense.
Accordingly, I dissent.
See footnotes 2 through 5 of the majority opinion.
While serving as a member of the Appellate Court, the author of the majority opinion in the present case signed his name to the following proposition: “It cannot be assumed that information relating to the mannerisms and tendencies of intoxicated [persons] is within the common knowledge of the average juror. State v. Holeman, 18 Conn. App. 175, 179, 556 A.2d 1052 (1989); see also State v. Grayton, 163 Conn. 104, 111, 302 A.2d 246, cert. denied, 409 U.S. 1045, 93 S. Ct. 542, 34 L. Ed. 2d 495 (1972).” State v. Kwaak, 21 Conn. App. 138, 156-57, 572 A.2d 1015, cert. denied, 215 Conn. 811, 576 A.2d 540 (1990).
The defendant in Barletta sought to elicit testimony that an eyewitness’ observations were the result of hallucinations. The defense expert was unable to say whether “a person under the influence of cocaine is more likely than not to experience the type of complex visual hallucinations that would affect the reliability of his or her observations . . . .” State v. Barletta, supra, 238 Conn. 321.
The proper inquiry is not whether August would have provided the best of all possible testimony. Instead, the question is simply whether the jury would have been better able to evaluate the defendant’s sole defense — that is, his claim .that he was unable to form the requisite mens rea — if it had been permitted to hear the testimony of apsychiatric expert. Because August knew about the behavioral effects of the drugs that compose illy and the jury probably did not, this latter question must be answered in the affirmative. “A party is not required to offer such proof of a fact that it excludes all other hypotheses; it is sufficient if the evidence tends to make the existence or nonexistence of any oilier fact more probable or less probable than it would be without such evidence. State v. Briggs, [179 Conn. 328, 333, 426 A.2d *186298 (1979), cert. denied, 447 U.S. 912,100 S. Ct. 3000, 64 L. Ed. 2d 862 (1980)] . . . .Evidence is not rendered inadmissible because it is not conclusive. All that is required is that the evidence tend to support a relevant fact even to a slight degree, so long as it is not prejudicial or merely cumulative. State v. Miller, [202 Conn. 463, 482, 522 A.2d 249 (1987)]; State v. Morrill, 197 Conn. 507, 548, 498 A.2d 76 (1985). . . . C. Tait & J. LaPlante, [Connecticut Evidence (2d Ed. 1988)] § 8.1.1, pp. 225-26. . . . State v. Prioleau, [235 Conn. 274, 305-306, 664 A.2d 743 (1995)].” (Internal quotation marks omitted.) State v. Kiser, 43 Conn. App. 339, 362, 683 A.2d 1021, cert. denied, 239 Conn. 945, 686 A.2d 122 (1996), cert. denied, 520 U.S. 1190, 117 S. Ct. 1478, 137 L. Ed. 2d 690 (1997); see State v. Willis, 221 Conn. 518, 522, 605 A.2d 1359 (1992) (“[e]vidence is admitted, not because it is shown to be competent, but because it is not shown to be incompetent” [internal quotation marks omitted]).
The majority emphasizes August’s testimony that “[i]lly is not like a prescription drug, so . . . the clinical presentation depends on how much [of] each of the individual ingredients you have . . . .” (Internal quotation marks omitted.) If we are to be swayed by this fact, then we must adopt the following bright line rule: juries may never have the benefit of expert psychiatric testimony in cases involving the effect of substances prepared by black market apothecaries. Both common sense and our recent opinion in Barletta compel us to reject this rule.
It is for this reason that the trial court’s abuse of discretion in the present case could not possibly have been harmless.
The majority correctly observes that the defendant “testified as to the behavioral changes he has experienced as a result of smoking illy.” On the subject of the clinical presentation of a narcotic substance, it is obvious that the jury would be more likely to credit the testimony of an expert in psychiatry than it would be to credit 1he testimony of a defendant eager to obtain an acquittal.