Following a jury trial in which he did not testify, defendant was convicted of sexual abuse in the first degree. He appeals, claiming that OEC 609 violates his constitutional rights to be heard in his own defense and to trial by an impartial jury. On defendant’s appeal, the Court of Appeals affirmed from the bench. State v. Busby, 104 Or App 306, 799 P2d 1155 (1990).
The part of OEC 609 on which defendant bases his constitutional attack provides:
“(1) For the purpose of attacking the credibility of a witness, evidence that the witness has been convicted of a crime shall be admitted if elicited from the witness or established by public record, but only if the crime (a) was punishable by death or imprisonment in excess of one year under the law under which the witness was convicted, or (b) involved false statement or dishonesty.”
OEC 609 mandates admission in evidence, if offered, of certain prior felony convictions of any witness “[f]or the purpose of attacking the credibility of’ the witness.1
Our decision on review turns on the threshold requirements for mounting a constitutional challenge to a rule of evidence. The dispositive question is: May a defendant attack OEC 609, relating to impeachment of the defendant by certain prior convictions, as violative of constitutional protections without demonstrating how the operation of the rule in the defendant’s case prevented or diminished enjoyment of those protections? We hold that such a demonstration is required. Because defendant did not show by offer of proof *295the substance of his proposed testimony that he contends was lost to him because of the rule of evidence and, thus, did not show how or whether his testimony might have contributed to his defense, we affirm.
Defendant was charged with first degree sexual abuse of a 15-year-old girl. Defendant moved pretrial to exclude evidence of his prior conviction for sexual abuse, arguing that, if evidence of his prior conviction were admitted, he would be “forced, because of the extreme prejudicial value of this evidence and the necessity that he testify on his own behalf, to waive trial by jury.”
The trial court ruled that evidence of the prior conviction would be admissible at trial if defendant became a witness. The trial court concluded:
“3. Defendant’s right to testify and to be heard is not itself directly affected by the admission of prior convictions for impeachment purposes. Defendant may still testify and state his version of the facts to a jury.
“4. Defendant will suffer no constitutional deprivation by the admission of the above-noted prior felony convictions.”
At the conclusion of the state’s case-in-chief, defendant renewed his motion to exclude evidence of the prior conviction. At that time, defendant asserted that he “is going to choose to exercise his right not to testify” because of the “fact” that the conviction would be used to impeach him. Prior to trial, defendant had said that he would waive jury trial. But after the court ruled that it would permit his prior conviction to be placed in evidence, he did not waive a jury. Instead, at trial, defendant took the position that the trial court’s ruling that the prior conviction would be admitted for impeachment was, in effect, a ruling that excluded his testimony because, if he testified, the impartiality of the jury would be destroyed when the jury heard of his prior conviction for sexual abuse.
Defendant did not explain, represent, or offer what his “excluded” testimony would have been, either in support of his pretrial motion nor later at the time of its renewal after *296the state presented its case-in-chief. Defendant did not testify. The jury was never apprised of defendant’s prior conviction. It returned a verdict of guilty.
Defendant contends that OEC 609 violates his rights to be tried by an impartial jury and to be heard under Article I, section 11, of the Oregon Constitution,2 and also his rights under the federal constitution to a fair trial by an impartial jury and to due process of law. Defendant states that his right to testify in his own defense was taken from him by that rule of evidence because, had he testified, evidence of his prior conviction of sexual abuse would have come before the jury “automatically” on the state’s offer of it. Defendant argues that, having heard the prior conviction evidence, the jury’s ability to decide the present charge impartially would be destroyed. Defendant concedes that instructions limiting the prior sexual abuse conviction evidence to impeachment, if such instruction is requested, would be available, OEC 105, but contends that the jury would not follow that limiting instruction, in part because the prior conviction was for the same offense.
Defendant asserts that OEC 609 violates the state and federal constitutional protections cited by mandating admission, if offered, of evidence for impeachment purposes of certain previous felony convictions without permitting prior ‘ ‘balancing’ ’ by the court of its probative value versus its prejudicial effect. He complains of the “wholesale admission” of a defendant’s prior convictions without consideration of their relevance or effect on the impartiality of the jury.
In his pretrial motion to exclude evidence of his prior conviction, defendant argued: “[I]t is imperative that [defendant] testify on his own behalf. There is no one else who can tell [defendant’s] side of the story.” As noted, defendant did not elaborate further about what his side of the story would be, nor did he make any representation or offer of proof. Defendant claims that the exercise of his right to speak *297in his own behalf was “chilled,” violating his Article I, section 11, right to be heard.
The trial court’s ruling, that the impeachment evidence was admissible, did not preclude defendant from testifying. The trial court so found. That is obviously accurate in a literal sense. Defendant’s choice, not the trial court’s ruling, resulted in the jury’s not hearing defendant’s testimony.
Moreover, defendant’s careful consideration of that choice was facilitated by the timing of the ruling. In State v. McClure, 298 Or 336, 340, 692 P2d 579 (1984) - a case decided under the former version of OEC 609(1) that provided for discretionary balancing of probative value versus prejudicial effect — the court wrote:
“We believe trial courts should rule on the admissibility of prior crime impeachment evidence as soon as possible after the issue is raised. It is only after a ruling on the admissibility of a conviction that the prosecutor and defense counsel can make an informed decision how to effectively try the case.”
We continue to approve that practice under the present version of OEC 609. This court has recognized that a defendant’s decision whether to testify has a significant impact on what questions to ask jurors during voir dire, what to say in opening statements, and the questioning of witnesses. See State v. McClure, supra, 298 Or at 340; State v. Foster, 296 Or 174, 183, 674 P2d 587 (1983) (reasons for seeking pretrial rulings are to obtain guidance on how to conduct voir dire and opening statements and to avoid contaminating the jury).
Defendant’s decision in this case not to testify, when to do so would entail exposure of his criminal record, was a component of his overall trial strategy. A defendant’s choice of strategy under the amended version of OEC 609 is no different than the choice that a defendant would have faced before the rule was amended to delete the trial court’s exercise of discretion. There always was a risk of impeachment by prior convictions.3
*298The testimony that defendant here chose not to present might or might not have been judged by the jury sufficient to support reasonable doubt. We have no way of considering what effect defendant’s testimony might have had. Under OEC 103(l)(b), when a trial court excludes testimony or other evidence, an offer of proof by the proponent of the evidence is required to preserve any claim of error related to what the evidence would have shown. State v. Olmstead, 310 Or 455, 459-60, 800 P2d 277 (1990); State v. Affeld, 307 Or 125, 128, 764 P2d 220 (1988).4
Adequate offers of proof are required to ensure that appellate courts are able to determine (1) whether it was error to exclude the evidence, and (2) whether any error was likely to have affected the result of the case. State v. Affeld, supra, 307 Or at 128. State v. McClure, supra, 298 Or at 341, quoting with approval United States v. Cook, 608 F2d 1175, 1186 (9th Cir 1979), cert den 440 US 1034 (1980), which set two requirements for an offer of proof:
“In future cases, to preserve the issue for review, a defendant must at least * * * (1) establish on the record that he will in fact take the stand and testify if his challenged prior convictions are excluded; and (2) sufficiently outline the nature of his testimony so that the trial court, and the reviewing court, can [intelligently consider the ruling].”
This court previously has required a defendant to comply with the second prong of the requirements for an adequate offer of proof. State v. Foster, supra. In order to protect his claim of error concerning that evidentiary ruling, the defendant in Foster entered in the trial record both his proposed question on cross-examination and the document to which it related. On review, this court held that defense counsel had adequately preserved the assignment of error. 296 Or at 183. This court determined, from the record made at the pretrial hearing, that admission of the evidence would have been prejudicial error. Id. at 184. See also State v. *299McClure, supra, 298 Or at 339-42, 350 (defense counsel’s offer of proof, by a representation advising trial court both (1) that the defendant would testify and (2) what his testimony would be, showing “the importance of defendant’s testimony,” was held sufficient for judicial review of trial court’s ruling on admissibility of impeachment evidence).5
Even if error occurs during trial, this court will not reverse a conviction if the error is harmless. In State v. Walton, 311 Or 223, 230, 809 P2d 81 (1991), this court reiterated the rule for testing harmless error under the Oregon Constitution, found in State v. Isom, 306 Or 587, 595-96, 761 P2d 524 (1988), as follows:
“Under Oregon law, a verdict against a criminal defendant may be affirmed notwithstanding trial error if the error did not affect a ‘substantial right’ of the defendant. OEC 103(1). This court has interpreted this to mean that the verdict may be affirmed if there is ‘little likelihood that the error affected the verdict.’ State v. Hansen, 304 Or 169, 180-81, 743 P2d 157 (1987); see also State v. Miller, 300 Or 203, 220-22, 709 P2d 225 (1985) [cert den 475 US 1141 (1986)].”
*300Defendant’s failure to place on the record what his trial testimony would have been has deprived this court of any basis for evaluating the gravity of the claimed error on which he relies.6 Because the record made at trial, lacking any offer of . proof, gives this court no foundation on which to determine whether defendant was prejudiced by the application of OEC 609, we do not reach defendant’s claim that his Article I, section 11, right to be heard was violated because of OEC 609’s mandatory provisions.
Next, defendant contends that OEC 609, as applied in this case, violated his right to trial by an impartial jury under Article I, section 11, of the Oregon Constitution. Defendant argues that, without a preliminary case-by-case balancing of probative value against prejudicial effect, man-datorily admitted evidence of a prior sexual abuse conviction for impeachment purposes probably will be so prejudicial to the defendant as to impair a jury’s ability to be fair and impartial. Defendant asks this court to accept as a universal fact that “[jjuries will conclude a defendant is guilty based upon his prior convictions” and that jury instructions on the proper use of prior convictions are futile.7
We acknowledge that the threat of potential prejudice from the introduction of impeachment evidence may create a dilemma for a defendant with regard to the decision whether to testify. But we decline either to presume harm to defendant, when nothing in the record casts doubt on the jury’s impartiality, or to assume that defendant was deprived of an impartial jury.
Defendant’s final contention is that the trial court’s application of OEC 609 violated his rights to a fair trial, an impartial jury, and due process of law under the Sixth and *301Fourteenth Amendments to the Constitution of the United States.8
We agree that the Sixth Amendment guarantee of a “trial by an impartial jury” is a basic requirement of due process, Irwin v. Dowd, 366 US 717, 722, 81 S Ct 1639, 6 L Ed 2d 751 (1961), and that the guarantee applies to state trials under the Fourteenth Amendment. Duncan v. Louisiana, 391 US 145, 148-49, 88 S Ct 1444, 20 L Ed 2d 491 (1968).
Defendant makes the same arguments under the federal constitutional provisions that he makes under Article I, section 11, of the Oregon Constitution, and its guarantee of an impartial jury. Our response is also the same; defendant has failed to present to this court a record offer of proof from which we could infer, even slightly, that the jury in defendant’s trial was not impartial or that his choice to not testify deprived him of some process that he was due.9 Trial error related to evidentiary rulings is usually subject to a harmless error analysis under the federal constitution, as well.10 That *302analysis cannot be performed with nothing on the record to show the effect of any claimed error.
Any supposed, but undisclosed, detriment that defendant suffered by failing to testify was produced by his choice to remain silent, a choice also constitutionally guaranteed. Defendant’s contentions present no grounds for reversal.
The decision of the Court of Appeals and the judgment of the circuit court are affirmed.
OEC 609 was amended by Oregon Laws 1987, chapter 2, section 9, adopted by the people at the 1986 general election. This court has construed those amendments to mandate admission of certain prior convictions, if offered. State v. King, 307 Or 332, 337-38, 768 P2d 391 (1989) (“balancingis impermissible;” constitutional issues not reached).
Former OEC 609 required that, before admitting evidence of previous felony convictions to impeach a witness, the trial court must first determine that the probative value of admitting the evidence outweighed its prejudicial effect to the defendant. ORS 40.355 (OEC 609) (1985). However, before the Oregon Evidence Code, including the original version of OEC 609, was adopted as Oregon Laws 1981, chapter 892, section 53, the rules of evidence used in this state did not require judicial balancing prior to admission of records of conviction to impeach a witness. ORS 45.600 (1979).
Article I, section 11, of the Oregon Constitution, provides in part:
“In all criminal prosecutions, the accused shall have the right to public trial by an impartial jury * * * to be heard by himself and counsel * *
A Comment, Sword and Shield: An Analysis of Criminal Defendants’ Right to Be Heard under Article I, section 11 of the Oregon Constitution, 28 Willamette L Rev 127 (1991), reviews some interpretations of Article I, section 11.
See State v. Minnieweather, 99 Or App 166, 169, 781 P2d 401 (1989), where the Court of Appeals repeated: “A defendant who testifies may constitutionally be subjected to cross-examination and impeachment * * *, State v. Deal, 52 Or 568, 98 P 165 (1908).”
A distinction must be made concerning a trial court’s rulings striking a claim or defense, as a matter of law. There an offer of proof is not required to preserve the legal issue of whether such a defense, itself already disclosed on the record, is available in the context of the case. State v. Olmstead, 310 Or 455, 459-60, 800 P2d 1277 (1990). Compare with State v. Clowes, 310 Or 686, 692, 801 P2d 789 (1990) (trial court may require offer of proof to make a relevancy determination, under OEC 104(1) and 401, as to whether a proffered defense is available as a matter of law).
OEC 103(l)(b) (except for plain errors affecting substantial rights) requires, where a claim of error is to be predicated on an evidentiary ruling, that:
“In case the ruling is one excluding evidence, the substance of the evidence was made known to the court by offer or was apparent from the context within which questions were asked.” (Emphasis added.)
Of course, the trial court’s ruling here would have admitted evidence, but defendant’s contention is that the ruling had the effect of excluding other evidence, i.e., defendant’s testimony. OEC 103(l)(b), as quoted, would apply to a claim of excluded evidence.
Where the error assigned on appeal is that favorable evidence has been excluded erroneously, Oregon case law prior to adoption of the evidence code in 1981 required an adequate offer of proof for reasons that continue to be valid under OEC 103. For example, in Livesleyv. Strauss, 104 Or 356,370,206 P 850, (1922), finding the offer inadequate, this court said:
“However, the questions asked the witness did not suggest the answer which would have been given if the witness had been permitted to answer, nor did the plaintiffs inform the court what the witness would have stated if permitted to testify; and consequently we cannot know whether the plaintiffs were injured by this ruling of the court.”
In Schweiger v. Solbeck, 191 Or 454, 474, 230 P2d 195 (1951), this court said:
“[Cjounsel should have made a proper offer of proof, not only to advise the trial court as to his position, but also so that this court on appeal might intelligently pass upon the trial court’s ruling.”
See also State v. Jenkins, 246 Or 280, 280-81, 424 P2d 894 (1967) (supreme court had “no way of determining whether the exclusion” of defendant’s evidence was prejudicial, without an offer of proof).
A defendant whose choice was to testify could still have claimed, as this defendant does, that state and federal constitutional rights to an impartial jury were violated by the trial court’s ruling admitting evidence of the prior conviction. Failure to testify is not required to preserve any of the constitutional claims, defendant urges here.
Defendant does not, nor can he on this record, argue that the jury impaneled for his own trial was influenced, improperly or otherwise, by the evidence of his prior convictions, because that evidence was never placed before the jury.
The Sixth Amendment to the Constitution of the United States provides in part:
“In all criminal prosecutions, the accused shall enjoy the right to a speedy and public trial, by an impartial jury * *
Section 1 of the Fourteenth Amendment to the Constitution of the United States, in part, provides:
“[N]or shall any State deprive any person of life, liberty, or property, without due process of law * *
Defendant also cites the Fifth Amendment as being applicable to his contentions but does not relate them specifically to the text of that amendment.
In order to raise and preserve error under FRE 609a, which, unlike the present version of OEC 609, requires a trial judge to balance probative value against prejudicial effect before admission of prior conviction impeachment evidence, a defendant must actually testify. Otherwise, it “would be a matter of conjecture whether” the trial court would, after balancing, have admitted the prior conviction for impeachment. Luce v. United States, 469 US 38, 42-43, 105 S Ct 460, 83 L Ed 2d 443 (1984).
See Arizona v. Fulminante, 499 US_,_, 111 S Ct 1246, 113 L Ed 2d 302, 329-31 (1991), compiling cases in which the Supreme Court of the United States has applied the harmless error analysis to errors in the trial process, but distinguishing errors involving “structural defects in the constitution of the trial mechanism, which defy analysis by ‘harmless-error’ standards.”
Where the harmless error inquiry is applied to direct appeals, the Supreme Court of the United States articulates the proper test as follows: “[Bjefore a federal constitutional error can be held to be harmless, the court must be able to declare a belief that the error was harmless beyond a reasonable doubt.” Chapman v. California, 386 US 18, 24, 87 S Ct 824, 17 L Ed 2d 705 (1967) (reconfirmed as the *302proper test in Yates v. Evatt, 500 US_, 111 S Ct 1884, 114 L Ed 2d 432 (1991), overruled on different grounds, Estelle v. McGuire,_US-, 112 S Ct 475, 116 L Ed 2d 385 (1991)).