The defendant, Calvin Woodburn, Sr., appeals from judgments of the Superior Court (Lincoln County, Bradford, J.) entered on jury verdicts finding him guilty of-gross sexual misconduct, 17-A M.R.S.A. § 253 (Supp.1988), and unlawful sexual contact, 17-A M.R.S.A. § 255 (Supp.1988). Woodburn contends that the trial court erred 1) in refusing to permit individual voir dire of the jurors, 2) by excluding expert testimony concerning the ability of the victim to distinguish truth from falsehood, and 3) in finding the victim competent to testify. Woodburn also asserts that the evidence was insufficient to sustain the convictions. We affirm the judgments.
I
A jury would have been warranted in finding, inter alia, the following facts: In June 1985 after the separation of Wood-burn from his wife, Woodburn and his two sons moved into his mother’s three-room home. Due to the limited living space in the home, Woodburn and his elder son, then six years old, shared a bed. At trial, the child testified that at night Woodburn subjected him to a number of sexual acts and incidents of sexual contact. Woodburn denied the allegations. He testified that he often awakened his son in the night to determine whether his son had urinated in the bed. In the fall of 1986, the child was placed in a foster home where he disclosed the sexual activity at issue.
The jury found Woodburn guilty of the charged offenses, and Woodburn appeals.
II
Initially, Woodburn contends that the trial court committed reversible error in refusing to permit Woodburn’s counsel to conduct an individual voir dire of the members of the jury panel. We disagree.
As a part of the voir dire, the trial court utilized a written confidential questionnaire, answered by the jurors under oath, that addressed the area of sexual abuse. A juror who responded affirmatively to any of the questions was excused for cause. Using seven of the nine questions proposed by Woodburn, the court also conducted an oral voir dire. As a group, the court questioned those jurors who had responded in the negative to the written questions as to other areas of potential bias. The remaining two questions proposed by Woodburn were deemed by the court to be repetitive and were not asked of the jury panel.
Woodburn argues that the use of the written questionnaire without further individual oral voir dire in the area of sexual abuse denied him the opportunity to evaluate the demeanor of each juror who gave negative answers to the questionnaire. He also argues that the court’s refusal of two of his proposed questions was error. We find no merit in either argument.
“The purpose of a voir dire examination is to detect bias and prejudice in prospective jurors, thus ensuring that a defendant will be tried by as fair and impartial a jury as possible.” State v. Lovely, 451 A.2d 900, 901 (Me.1982). Considerable discretion over the conduct and scope of juror voir dire is vested in the trial court, which has the responsibility of balancing the competing considerations of fairness to the defendant, judicial economy, and avoidance of embarrassment to potential jurors. State v. Waterhouse, 513 A.2d 862, 863 (Me.1986); State v. Robbins, 401 A.2d 161 (Me.1979). “On appeal, the decision of the trial court will be reversed only for an abuse of discretion.” State v. Durost, 497 A.2d 134, 136 (Me.1985). Although cases involving allegations of sexual abuse of a child are potentially ripe for juror bias, we have expressly rejected the proposition that individual voir dire be mandated in all such cases. Id. See State v. Weymouth, 496 A.2d 1053 (Me.1985) (trial justice need not inevitably resort to private questioning in a case of sexual abuse of a minor); see also State v. Lambert, 528 A.2d 890, 892 (Me.1987) (trial court did not abuse its discretion by refusing to allow defendant to individually voir dire prospective jurors concerning possible bias against homosexuals).
*345In the instant case we conclude there was no abuse of discretion in the trial court’s decision to put in written form those questions dealing with matters of potential embarrassment to the jurors. An affirmative response to any question required the revelation by a juror of sensitive personal or family history. This form of inquiry did not impair the defendant’s ability to discover prejudice, if any, that a potential juror may have had concerning the subject matter of the charges against Woodburn. Nor did the court abuse its discretion in refusing two of the questions proposed by Woodburn for the oral voir dire of the jury. Our review of the record discloses the questions were clearly repetitive of questions posed in the written questionnaire. State v. Weymouth, 496 A.2d at 1055; see also State v. Lambert, 528 A.2d at 892.
Ill
Woodburn also contends that the trial court erred in excluding the opinion of Woodburn’s expert witness, Paul Sobchuk, a clinical psychologist, that the victim was unable to distinguish truth from falsehood. We disagree.
Over the objection of the State,1 Wood-burn sought to introduce the testimony of Sobchuk that he had met with the child for twenty-four, one-hour sessions between September 1985 and June 1986 for reasons not connected with this case, although coincidentally throughout the period of the alleged abuse. The child had been referred to Sobchuk for the purpose of evaluating the child’s competency because he was “acting out” and not doing well at school. Sobchuk had questioned the child on several topics including fighting, relationships with other children and disciplinary action at home. Sobchuk had then checked with others to determine the accuracy of the child’s responses. By this method Sobchuk had concluded that the child had lied on a number of occasions; that he could be easily led and would lie to please an examiner. Such behavior, he opined, demonstrated an “inability to distinguish truth from falsehood” which was a “medically recognized syndrome somewhat akin to” what is listed in the Diagnostic and Statistical Manual of Mental Disorders III (DSM III) as “conduct disorder, unsocialized aggressive.” The DSM III was not introduced into evidence nor was there any other reference to it by Sobchuk. He stated that the child had not discussed any sexual abuse during his sessions with Sobchuk, but had the child done so he “would still have strong suspicions of whether or not [the child] had been sexually abused,” because of his experience with the child.
Relying primarily on M.R.Evid. 404(b) and 702 and the discretionary power of the court pursuant to Rule 403, the trial court excluded that portion of Dr. Sobchuk’s testimony that proffered his expert opinion relating to the child’s “inability to distinguish truth from falsehood.”
Here, the testimony in issue is the opinion of Sobchuk, based on specific incidents of conduct of the child, that the child had lied in the past and that he was unable to distinguish truth from falsehood. This proffered opinion clearly embraced the ultimate issue to be decided by the jury as to the truthfulness of the child’s testimony relating to his alleged sexual abuse by Woodburn. Thus, the issue presented for review is whether the trial court properly determined the testimony was inadmissible under the Rules of Evidence.
If otherwise admissible, M.R.Evid. 704 provides for the admissibility of testimony in the form of an opinion on an ultimate issue to be decided by the jury subject to Rules 701 (opinion of witness not testifying as expert) and 702 (opinion of expert witness) that the opinion must be helpful to the trier of fact; and subject further to the discretion of the court, under Rule 403, to exclude opinions if the probative value is outweighed by the danger of unfair prejudice or confusion, or would be a waste of time, or would mislead the jury. See R. Field & P. Murray, Maine Evidence § 704.1 (2d ed.1987).
*346Under M.R.Evid. 702, before admitting expert testimony the trial court must consider (1) whether the matter is beyond common knowledge so that the untrained layman will not be able to determine it intelligently and (2) whether the witness is qualified to give the opinion sought. R. Field & P. Murray, supra, § 702.1 at 263; State v. Boutilier, 426 A.2d 876, 878 (Me.1981).
Although the expert need not be able to state his opinion with any special degree of certainty, he must be able to provide some insight beyond the kind of judgment an ordinarily intelligent juror can exert. See State v. Fernald, 397 A.2d 194, 197 (Me.1979); State v. Lewisohn, 379 A.2d 1192, 1203 (Me.1977). In determining whether the proffered testimony will be relevant and helpful, the trial court may consider whether the scientific matters involved in the testimony have been generally accepted and whether the testimony has been demonstrated to have sufficient reliability as a predictor of untruthfulness. See State v. Black, 537 A.2d 1154 (Me.1988); State v. Philbrick, 436 A.2d 844 (Me.1981).
Rule 404(b) provides that evidence of other crimes, wrongs or acts is not admissible to prove the character of a person in order to show that on a particular occasion he acted in conformity therewith. The credibility of a witness may be attacked by evidence of his reputation for truthfulness or untruthfulness rather than by evidence of his character generally, M.R.Evid. 608(a), or, within limits, and subject to the discretion of the court, on cross-examination by questioning a principal witness, such as the child victim in this case, or a character witness about specific incidents of conduct. M.R.Evid. 608(b).
Throughout the extensive voir dire Sob-chuk never identified the “medically recognized syndrome” to which he alluded, other than by the vague reference that it was “akin to conduct disorder, unsocialized aggressive.” He at no time stated whether the “syndrome” was listed in any DSM used by mental health professionals or what, if any, were the criteria for its diagnosis. Sobchuk’s testimony demonstrates no scientifically accepted basis for determining that the child was unable to distinguish truth from falsehood. The fact that he may have lied on unrelated occasions was not demonstrated to be a reliable predictor that he was lying on this occasion. See State v. Black, 537 A.2d at 1157. Thus, the trial court could properly determine that the testimony did not meet the requirements of M.R.Evid. 702 and, therefore, was inadmissible under M.R.Evid. 704. The proffered testimony was not offered as evidence of the child’s reputation for truthfulness, M.R.Evid. 608(a), nor were the specific incidents of the child’s past lying elicited through the cross-examination of the child or of a character witness. M.R.Evid. 608(b). The effect of the testimony, if admitted, would be to evade the limitations of M.R.Evid. 404(b) and 608(a) and (b). See State v. Arnold, 421 A.2d 932 (Me.1980) (psychologist’s testimony regarding defendant’s truthfulness was inadmissible character evidence). Accordingly, we hold that the trial court did not abuse its discretion in excluding the proffered opinion of Dr. Sobchuk as to the truthfulness of the child.
IV
Woodburn next contends that the court erred in its determination that the eight-year-old child victim was competent to testify.2 We disagree. As we stated in State v. Hussey, 521 A.2d 278 (Me.1987), we review the trial court’s finding that a witness has met the requirements of Rule 601(b) to determine if such finding is clearly erroneous.3 The record in the instant *347case discloses sufficient evidence to support the trial court’s finding that the child demonstrated an ability to express himself and make himself understood to the court and jury and had a sufficient understanding of the duty to tell the truth and was therefore competent to testify. M.R. Evid. 601(b); State v. Hussey, 521 A.2d at 280.
Finally, Woodburn challenges the sufficiency of the evidence supporting his convictions. Our review discloses that viewing the evidence in a light most favorable to the prosecution, any trier of fact rationally could find beyond a reasonable doubt every element of the offenses charged. State v. Barry, 495 A.2d 825 (Me.1985).
The entry is:
Judgments affirmed.
McKUSICK, C.J., and ROBERTS, WATHEN and CLIFFORD, JJ., concur.
. The State did not object to Paul Sobchuk's qualification as an expert.
. Woodburn did not offer the testimony of Dr. Sobchuk to challenge the child’s competence as a witness.
. Prior to our decision in Hussey and in reliance on cases decided before the promulgation of Rule 601 on February 2, 1976, we mistakenly set forth the standard for appellate review as being the determination of whether the trial court had abused its discretion. See State v. Emery, 434 A.2d 51, 52 (Me.1981); State v. Vigue, 420 A.2d 242, 246 (Me.1980), State v. Pinkham, 411 A.2d 1021, 1024 (Me.1980).