ZIMMERMAN, Justice:
Defendant Richard M. Eldredge appeals from his jury conviction of four counts of sodomy on a child, in violation of section 76-5-403 of the Code. He makes several claims of error relating to, inter alia, the following: admission of the child victim’s testimony and hearsay statements, exclusion of polygraph evidence and evidence of a witness’s bias, sufficiency of the evidence, and failure to grant a motion for a new trial or an arrest of judgment based on exculpatory evidence discovered after trial. We affirm.
When Eldredge’s son was two years old, Eldredge and the boy’s mother, Suzanne Sanchez, separated and then divorced. Sanchez was awarded custody of their son, and Eldredge was granted visitation rights. At a hearing held a year and a half later, Sanchez unsuccessfully sought modification of the divorce decree to reduce the frequency of Eldredge’s visits. Within a few months of the hearing, Sanchez reported to the sheriff’s office that she suspected Eldredge of sexually abusing their son.
Shortly after that report was made, Thomas Harrison, a social worker and director of the Child Sexual Abuse Program in the Department of Psychiatry at Primary Children’s Medical Center, interviewed the boy and concluded that he was probably the victim of sexual abuse. Harrison immediately reported this conclusion to the sheriff’s office and began treating the child, which he continued to do for approximately one year.
Eldredge was charged and tried on four counts of sodomy on a child, a first degree felony. See Utah Code Ann. § 76-5-403 (Supp.1979). At trial, several witnesses, including the victim, the victim’s mother, and Harrison, testified for the prosecution. The boy, then five years old, used anatomically correct dolls to demonstrate his testimony of oral sexual abuse. Although his testimony was somewhat confused and contradictory, the boy did state that he was telling the truth when he testified that Eldredge had committed the oral sodomy.
Sanchez testified that her son had exhibited bizarre behavior and symptoms of illness shortly after returning from various visits with Eldredge. Specifically, she said that on one occasion, the child told her to look at and taste his penis because it tasted good. And on several occasions after vis[31]*31its, the boy demonstrated disassociative behavior such as lapsing into unresponsive states during which he removed all of his clothing and pretended to be a dog, appeared to be stunned, or sobbed uncontrollably. Immediately after visits, the child was often pale and vomited or had diarrhea, according to Sanchez’s testimony.
Harrison testified that when he and the child discussed sexual abuse, the boy exhibited the same types of disassociative behavior and symptoms described by Sanchez. The child lapsed into various imaginary animal characterizations and expressly refused to be himself. He suffered from enuresis and encopresis (uncontrolled urination and defecation) and attributed his behavior to the imaginary animals. Harrison then discussed professional literature on child sexual abuse, compared the boy’s behaviors and symptoms to those described in the literature, and concluded that they were consistent with the child’s having been the victim of sexual abuse.
Harrison also testified that during their therapy sessions, the boy had described and demonstrated the physical acts of abuse by using anatomically correct dolls and had attributed the abuse to Eldredge. Harrison repeated various other out-of-court statements made to him by the boy, such as the child’s description of El-dredge’s erection and ejaculation. He testified that such a young child’s ability to describe and demonstrate sexual acts strongly indicated personal exposure to and involvement in those acts and that in his opinion, the boy was the victim of sexual abuse. Finally, he testified that it was his opinion that the child’s statements made during therapy were truthful, including his statements attributing the sexual abuse to Eldredge.
Several witnesses testified for the defense. Eldredge took the stand and denied the abuse. The jury found him guilty, in October 1984, on all four counts. The trial court sentenced him to four concurrent terms of imprisonment, each for five years to life, under the first degree felony sentencing provisions of the Code. See Utah Code Ann. §§ 76-3-203(1) (1978). Eldredge appeals. We will consider his claims of error seriatim.
Eldredge first asserts that the trial court’s retroactive application of sections 76-5-410 and -411 of the Code ran afoul of the federal ban on ex post facto laws because it operated to narrow the scope of his federal constitutional right to confront the witnesses against him.1 See U.S. Const, art. I, § 10, amends. VI, XIV. Section 76-5-410 provides that a child victim of sexual abuse shall be considered competent to testify at trial without prior qualification.2 Utah Code Ann. § 76-5-410 (Supp.1983). Section 76-5-411 makes such a child’s out-of-court statements regarding the abuse admissible if certain requirements are met, even if the evidence would otherwise be inadmissible hearsay.3 Utah Code Ann. [32]*32§ 76-5-411 (Supp.1983). Pursuant to these statutes, the child, who was five years old at the time of trial, testified and some of his out-of-court statements were admitted. Eldredge terms the trial court’s reliance on sections 76-5-410 and -411 “ex post facto” because those statutes became effective after the crimes were committed but before the trial.
The first step in resolving this claim is to determine the scope of the federal constitutional prohibition against ex post facto laws. The United States Supreme Court has defined as ex post facto any law that operates to make criminal an act that was innocent when done, to increase the punishment for a crime after its commission, or to allow conviction on less proof in amount or degree than was required when the offense was committed.4 See Dobbert v. Florida, 432 U.S. 282, 292-94, 97 S.Ct. 2290, 2297-99, 53 L.Ed.2d 344 reh’g denied, 434 U.S. 882, 98 S.Ct. 246, 54 L.Ed.2d 166 (1977); Beazell v. Ohio, 269 U.S. 167, 169-70, 46 S.Ct. 68, 68-69, 70 L.Ed. 216 (1925); Thompson v. Missouri, 171 U.S. 380, 383-85, 387, 18 S.Ct. 922, 923-24, 924-25, 43 L.Ed. 204 (1898); Hopt v. Utah, 110 U.S. 574, 589-90, 4 S.Ct. 202, 209-10, 28 L.Ed. 262 (1884). Under this definition, “Statutes which simply enlarge the class of persons who may be competent to testify in criminal cases are not ex post facto in their application to prosecutions for crimes committed prior to their passage.” Hopt, 110 U.S. at 589, 4 S.Ct. at 210; accord Underwood v. State, 111 Tex.Crim. 124, 125, 12 S.W.2d 206, 206 (1927); State v. Clevenger, 69 Wash.2d 136, 140-42, 417 P.2d 626, 629-30 (1966); State v. Slider, 38 Wash.App. 689, 693-95, 688 P.2d 538, 541-42 (1984) (statute similar to section 76-5-411). Similarly, the retroactive application of statutes that make previously inadmissible evidence admissible is not ex post facto. Thompson, 171 U.S. at 385, 387, 18 S.Ct. at 924, 924-25, reaffirmed in Beazell, 269 U.S. at 170-71, 46 S.Ct. at 68-69.
We must examine sections 76-5-410 and -411 in light of these rules to determine whether their application was ex post facto. Section 76-5-410 allows children to testify who might otherwise have been disqualified under prior law. See State v. Fulton, 742 P.2d 1208, 1217 (Utah 1987), cert. denied, — U.S. -, 108 S.Ct. 777, 98 L.Ed.2d 864 (1988). On its face, section 76-5-410 can be characterized as merely enlarging the class of persons competent to testify. And section 76-5-411 appears to do no more than allow the admission of otherwise inadmissible hearsay statements. Therefore, sections 76-5-410 and -411 do not appear to fall within the Supreme Court’s definition of ex post facto laws.
Eldredge, however, argues that the Supreme Court has stated that the ex post facto provision prohibits retroactive application of laws that operate to deny a substantial right in existence when the crime was committed. See Weaver v. Graham, 450 U.S. 24, 29 n. 12, 101 S.Ct. 960, 964 n. 12, 67 L.Ed.2d 17 (1981); Thompson v. Utah, 170 U.S. 343, 354-55, 18 S.Ct. 620, 624, 42 L.Ed. 1061 (1898); Kring v. Missouri, 107 U.S. 221, 232, 235-36, 2 S.Ct. 443, 452, 454-55, 27 L.Ed. 506 (1883). He contends that the application of sections 76-5-410 and -411 to his case was prohibited by the ex post facto provision because it [33]*33actually operated to deny his federal constitutional right to confrontation as it existed at the time the crimes were committed.
First, Eldredge contends that allowing his son to testify pursuant to section 76-5-410 effectively denied him his right to confrontation because when the boy took the stand, as the statute permitted, his testimony was so equivocal and confused as to make meaningful cross-examination impossible. We disagree. A review of the record demonstrates that Eldredge’s cross-examination was very effective, so effective that the child recanted and denied the abuse. Therefore, we conclude that section 76-5-410 did not operate to deny El-dredge’s federal confrontation right. See State v. Marcum, 750 P.2d 599, 602-03 (Utah 1988).
Second, Eldredge argues that admission of his son’s out-of-court statements pursuant to section 76-5-411 violated his right to confrontation because he could not effectively cross-examine the boy. This Court has held on several occasions that the admission of such hearsay does not abridge a defendant’s right to confrontation if the child victim is present and available to testify and be cross-examined. Marcum, 750 P.2d at 603; State v. Loughton, 747 P.2d 426, 429 (Utah 1987); State v. Fulton, 742 P.2d at 1218-19; State v. Nelson, 725 P.2d 1353, 1356 (Utah 1986). Moreover, here the child actually testified and was cross-examined quite effectively. Finally, this argument, like Eldredge’s argument with respect to section 76-5-410, has previously been rejected on similar facts. See Marcum, 750 P.2d at 602-03; Loughton, 747 P.2d at 429-30; Fulton, 742 P.2d at 1210-11, 1218-19 & n. 16; Nelson, 725 P.2d at 1356-57.
Because the Supreme Court’s definition of ex post facto laws does not encompass sections 76-5-410 and -411 and because we do not find a denial of Eldredge’s right to confrontation, we reject his claim that their application to his case offended the ex post facto ban.5
Eldredge next claims that even if sections 76-5-410 and -411 can be applied to his case, the trial court misinterpreted their requirements and, as a result, misapplied both sections. We first address El-dredge’s section 76-5-410 challenge, which is based on Utah Rule of Evidence 602.
Rule 602 states that a witness may testify only to those matters of which he or she has personal knowledge.6 Eldredge contends that under this rule, testimony of a witness must be excluded if the witness’s memory of the subject matter of the testimony is less than complete. He argues that his son’s testimony indicated that the boy had virtually no memory of the events charged. Therefore, Eldredge concludes, the child’s testimony should have been excluded.
Rule 602 is not amenable to such a broad construction. It merely requires that the witness have the opportunity and the capacity to perceive the events in question. See State v. Calamity, 735 P.2d 39, 42 (Utah 1987); Utah R.Evid. 602; Fed.R. Evid. 602 advisory committee’s note; J. Weinstein & M. Berger, Weinstein’s Evidence ¶ 602[02] (1987). Here there is no contention that the boy lacked personal knowledge of the incidents of abuse; the only question is how well he could remember the details.
We have previously explained, in a case dealing with the competency of a child sexual abuse victim, that lapses in memory are appropriately dealt with under Utah Rule [34]*34of Evidence 403, which provides for the exclusion of testimony so unreliable that its potential for unfair prejudice substantially outweighs its probative value. See State v. Fulton, 742 P.2d at 1218 & n. 15; Utah R.Evid. 403; J. Weinstein & M. Berger, Weinstein’s Evidence ¶ 601[04] (1987). Because Eldredge did not object to the child’s testimony on rule 403 grounds either below or on appeal, we decline to address the question of whether his testimony should have been excluded under that rule.
Next, we address Eldredge’s claim that the trial court, in admitting the boy’s out-of-court statements, misinterpreted and misapplied section 76-5-411. As it read at the time of Eldredge’s trial, that section required the trial court to determine whether the child victim’s out-of-court statements satisfied one of two alternative tests contained in subparts (1) and (2) of subsection 76-5-411(1), as well as the test contained in the last two sentences of that subsection. State v. Nelson, 725 P.2d at 1355 n. 3. Subparts (1) and (2) required either that the child testify or that other corroborative evidence of the abuse exist. The last two sentences of subsection 76-5-411(1) required the trial judge to determine whether the interests of justice would be served by admission of the statement and to consider the child’s age and maturity, the nature and duration of the alleged abuse, the child’s relationship to the accused, the statement’s reliability, and the child’s reliability. Utah Code Ann. § 76-5-411 (Supp. 1983) (quoted in footnote 3, supra).
As we observed in Nelson, the trial court must consider not only the factors listed in subsection 76-5-411(1), but also any other factors pertinent to a careful evaluation of the reliability of the out-of-court statements.
Subsection 76-5-411(1) ... addresses the trustworthiness [of a child victim’s hearsay statements] by listing a number of factors the trial judge must consider before admitting such evidence. These factors are intended to prompt a comprehensive inquiry into all the circumstances surrounding the child’s out-of-court statement in order to determine its reliability. It is noteworthy that subsection 76-5-411(1) requires a determination of reliability without regard to ... the hearsay [declarant’s availability]. The importance of such an inquiry cannot be overemphasized.
In any case involving a proffer of hearsay statements by a child victim, the trial court must make an in-depth evaluation of the proposed testimony as required by subsection 76-5-411(1). This inquiry may require consideration of some matters not specifically mentioned in the statute. For example, to determine the reliability of the statement, a court should consider how soon after the event it was given, whether the statement was spontaneous, the questions asked to elicit it, the number of times the statement was repeated or rehearsed, and whether the statement is reproduced verbatim in court, viz., tape recording, video tape, or otherwise.
725 P.2d at 1355 n. 3 (citing Unif.R.Evid. 807 (1986 amendment to 1974 Unif.R.Evid.) (promulgated by National Conference of Commissioners on Uniform State Laws)).
After considering all the relevant factors, the court must make written findings and conclusions with respect to each factor.
The trial court should then enter findings and conclusions regarding each of the factors listed in the statute to explain its reasons for admitting or excluding the testimony. Only when these steps are taken can a defendant be assured that the statutorily required appraisal has been made. Further, only when such steps are taken can this Court properly perform its appellate review function.
Nelson, 725 P.2d at 1355 n. 3.
The trial court in this case did not make the required findings, and Eldredge now apparently contends that the child’s statements should not have been admitted absent the findings. However, Eldredge neither requested that the Nelson findings be made nor objected to the admission of hearsay in their absence. Utah Rule of Evidence 103(a) requires “a clear and definite objection” at trial to preserve an evidentia-[35]*35ry error for appeal. See State v. Malmrose, 649 P.2d 56, 58 (Utah 1982) (decided under former Utah Rule of Evidence 4, a predecessor to rule 103).
In an attempt to meet that requirement, Eldredge points out that his counsel did object to admission of the victim’s testimony in the absence of a specific determination that the victim was competent to testify. The findings required by section 76-5-411 relate to the reliability of a victim’s out-of-court statements, which is by no means equivalent to the victim’s competency to testify at trial. State v. Fulton, 742 P.2d at 1219 n. 16. An objection based on competency does not call the trial court’s attention to the reliability issue. See id.; cf. State v. McCardell, 652 P.2d 942, 947 (Utah 1982) (foundation objection did not direct trial court’s attention to potential prejudice). Therefore, we conclude that no proper objection was made on this issue. In the absence of an adequate objection, the error in applying section 76-5-411 cannot be considered on appeal. Marcum, 750 P.2d at 603.
Despite the failure to properly preserve the issue below, Eldredge argues that we should reach the merits of his claim because admitting the testimony without making the required findings was plain error. Utah Rule of Evidence 103(d) provides: “Nothing in this rule precludes taking notice of plain errors affecting substantial rights although they were not brought to the attention of the court.” 7 The first requirement for a finding of plain error is that the error be “plain,” i.e., from our examination of the record, we must be able to say that it should have been obvious to a trial court that it was committing error. See State v. Poe, 21 Utah 2d 113, 117-18, 441 P.2d 512, 514-15 (1968), appeal after remand, 24 Utah 2d 355, 471 P.2d 870 (1970); State v. Cobo, 90 Utah 89, 102, 60 P.2d 952, 958 (1936); cf. State v. McCardell, 652 P.2d at 947 (incorrect objection did not bring error to trial court’s attention; not plain error under former rule 4). The second and somewhat interrelated requirement for a finding of plain error is that the error affect the substantial rights of the accused, i.e., that the error be harmful.8 See State v. Bullock, 699 P.2d 753, 756 (Utah 1985); State v. Lesley, 672 P.2d 79, 81-82 (Utah 1983); State v. Gardunio, 652 P.2d 1342, 1344 (Utah 1982) (per curiam); State v. Poe, 21 Utah 2d at 117-18, 441 P.2d at 515; State v. Cobo, 90 Utah at 102, 60 P.2d at 958.9
We first address the question of the error’s plainness. The rule that an error not called to the trial court’s attention will be [36]*36considered only if it can be shown to have been “plain” permits rule 103(d) and rule 103(a) to coexist. The principle underlying rule 103(a)’s requirement of “a timely objection ..stating the specific ground of objection” is that in the interest of orderly procedure, the trial court ought to be given an opportunity to address a claimed error and, if appropriate, correct it. See McCardell, 652 P.2d at 947. Normally, compliance by counsel with the contemporaneous objection requirement of rule 103(a) is assured because of the severe sanction that follows non-compliance: a refusal by the appellate court to consider the issue. However, the premise of rule 103(d) is that the ends of justice must not be lost sight of in the pursuit of procedural regularity and that when an error is plain, a trial court can legitimately be said to have had a reasonable opportunity to address and correct it, even in the absence of an objection.
In light of the purposes of the plainness requirement, can it fairly be said that the erroneousness of admitting the hearsay evidence without having first made the required findings should have been obvious to the trial court? The language of section 76-5-411 does not expressly require written findings regarding reliability, and the trial court did not have the benefit of an appellate decision interpreting the statute’s requirement — Nelson had not yet been decided. See United States v. Petrozziello, 548 F.2d 20, 23 (1st Cir.1977). We cannot conclude that the need for written findings should have been obvious. However, there is another closely related ground for exclusion that may form a basis for Eldredge’s claim of error. Utah Rule of Evidence 403 requires the exclusion of evidence if its potential for unfair prejudice substantially outweighs its probativeness. Under that rule, the question is whether the hearsay evidence was sufficiently unreliable that it should have been obvious to the trial judge ■that the testimony's probativeness was substantially outweighed by its potential for unfair prejudice. On this record, we cannot say “yes.”10
Being unable to find that either the need for findings or the fact that the evidence’s probativeness was outweighed by its potential for unfair prejudice should have been apparent to the trial court, we need not reach the second prong of the plain error rule — whether the admission of hearsay had a substantial impact on the verdict.11 And, because we do not find plain error, we do not reach the merits of Eldredge’s claim.12
Eldredge next claims that the victim’s therapist, Thomas Harrison, should not have been qualified as an expert in the diagnosis and treatment of child sexual abuse because he is a social worker rather than a psychiatrist or psychologist. Under Utah Rule of Evidence 702, trial courts have discretion in determining the qualifi[37]*37cations of expert witnesses. See, e.g. State v. Espinoza, 723 P.2d 420, 421 (Utah 1986); G. Joseph, S. Saltzburgh & The Trial Evidence Committee of the American Bar Association Section of Litigation, Evidence in America: The Federal Rules in the States § 51.3, at 2 (1987). And attaining a particular academic degree may be irrelevant to the substance of the necessary training and experience. E.g., Jenkins v. United States, 307 F.2d 637, 644 (D.C.Cir.1962) (en banc); Madison Granite Co. v. Industrial Comm’n, 138 Ariz. 573, 575-77, 676 P.2d 1, 3-5 (Ariz.App.1983); 3 J. Weinstein & M. Berger, Weinstein’s Evidence 11702[04], at 702-25, 702-51 (1987). Our review of the record convinces us that Harrison has extensive qualifications in this area of expertise and that the trial court did not abuse its discretion by allowing him to testify.13
Eldredge next claims that the trial court should have admitted the results of polygraph examinations that he took which would have bolstered his claim of innocence. A stipulation between the State and the accused is presently required for the admission of polygraph test results. State v. Fulton, 742 P.2d at 1212; State v. Abel, 600 P.2d 994, 998-99 (Utah 1979). The reason for this rule is that polygraph data has not been shown to be sufficiently reliable to justify the tendency of a fact finder to be overawed by the test results and too willing to abdicate its difficult truth-finding function to an expert and his or her machine. See Fulton, 742 P.2d at 1212; Abel, 600 P.2d at 996-97; Utah R.Evid. 403, 702. The rationale for admitting polygraph results with a stipulation is not that the stipulation makes them any more reliable or any less likely to dominate the fact-finding process, but that it serves as a waiver. Id. at 997. There was no waiver in this case because the State refused to stipulate to admission of the polygraph results. Therefore, under Fulton and Abel, the results were inadmissible.
Eldredge nevertheless argues that the polygraph results should have been admitted as a quid pro quo to balance the testimony of Thomas Harrison, who, in essence, functioned as a human lie detector when he testified as to the credibility of the victim’s out-of-court statements. Harrison’s opinion that the child’s statements were truthful was not a proper subject for testimony. However, the appropriate way for Eldredge to address the problem of Harrison’s testimony would have been to raise an objection and seek to exclude it, not to attempt to counter the testimony with his own inadmissible polygraph evidence. We must reject his argument for the admission of the polygraph evidence.
Eldredge next argues that the trial court erred when it limited the evidence demonstrating the bias of the victim’s mother, Suzanne Sanchez. Eldredge contends that he was not permitted to cross-examine Sanchez adequately or to present direct evidence that she was motivated to testify against him by a bitter visitation dispute. In State v. Hackford, 737 P.2d 200, 203 (Utah 1987), we held that evidence of prior conduct showing a witness’s bias or motive to testify falsely is admissible under Utah Rule of Evidence 608(c), subject to possible exclusion under Utah Rule of Evidence 403 if its potential for unfair prejudice outweighs its probativeness. We also noted that under some circumstances, the improper exclusion of such evidence may violate not only rule 608(c), but also the right to confrontation guaranteed by the federal constitution. Id. at 204; see Delaware v. Van Arsdall, 475 U.S. 673, 674, 677-79, 106 S.Ct. 1431, 1433, 1434-35, 89 L.Ed.2d 674 (1986); U.S. Const. amends. VI, XIV.
A review of the record in this case reveals neither an abuse of discretion in applying the evidentiary rules nor a violation of the constitutional right to confrontation. Defense counsel was allowed to introduce evidence of the visitation dispute, including evidence of Sanchez’s failure to make any allegations of sexual abuse until after she had been ordered to allow Eldredge his visitation rights. In closing argument, defense counsel stressed heavily Sanchez’s [38]*38purported bias against Eldredge and her motive to testify falsely, which resulted from the visitation battle. Under these circumstances, the trial court did not abuse its discretion or violate Eldredge’s right to confrontation by refusing to allow cumulative evidence on this issue. See Utah R.Evid. 403.
Moreover, even if it could be said that the trial court had erred, any error was waived. When the issue of the visitation dispute came up and the State objected to defense counsel’s continuing the line of questioning, the court stated that it was unwilling to allow counsel to elicit very much testimony on the visitation dispute, but that it would rule on the evidence’s admissibility on a question-by-question basis. The trial court then admonished counsel to make a record by asking the questions. After all this, defense counsel simply desisted in this line of questioning, thus effectively waiving this claim. See Utah R.Evid. 103(a).
Eldredge next asserts that the evidence at trial was insufficient to support the jury’s verdict. In evaluating such a claim, we must view the record evidence in the light most favorable to the verdict. State v. Speer, 718 P.2d 383, 384-85 (Utah 1986) (citing State v. Petree, 659 P.2d 443, 444 (Utah 1983)); State v. Lamm, 606 P.2d 229, 231 (Utah 1980); State v. Booker, 709 P.2d 342, 345 (Utah 1985). Having reviewed the evidence in that light, we cannot say that as a matter of law, the evidence was insufficient to sustain the verdict.
Eldredge next asserts that even if not one of the errors he complains of requires reversal, their cumulative effect denied him a fair trial. The concept of reversible cumulative error does not apply to this case because we have been unable to find any error. See State v. Bishop, 753 P.2d 439, 489 (Utah 1988); State v. Rammel, 721 P.2d 498, 501-02 (Utah 1986). We have rejected the claims of error reached on the merits, and we have found that the remaining claims were waived.
Finally, Eldredge claims that the trial court erred in refusing to order a new trial or to arrest the judgment. He asserts that the court should have granted him such relief because Thomas Harrison, who played an important role in the State’s case, stated after the conclusion of the trial that he was unsure of Eldredge’s guilt. At trial, Harrison was not asked and did not express an opinion as to Eldredge’s guilt. The bulk of his testimony related to his conclusion that the child had been abused by someone, although not necessarily by Eldredge. He did testify that the victim attributed the abuse to Eldredge and that he had no reason to doubt the child’s truthfulness. The gist of Eldredge’s argument is that the State knew of Harrison’s doubts about Eldredge’s guilt and should have informed Eldredge so that he could have brought out Harrison’s uncertainty at trial to create a reasonable doubt. Therefore, the meritoriousness of Eldredge’s claim depends on the admissibility of Harrison’s opinion regarding Eldredge’s guilt.
The standards for arresting a judgment or granting a new trial are set out in Utah Rules of Criminal Procedure 23 and 24(a). Rule 23 requires a trial court to arrest judgment on the motion of the accused if the facts proved at trial do not constitute a crime, if the accused is mentally ill, or for “other good cause.” Utah R.Crim.P. 23. Rule 24(a) allows a trial court to grant a new trial on the motion of the accused if any error or impropriety in the trial had a “substantial adverse impact” on the rights of the accused. Utah R.Crim.P. 24(a). The question, then, is whether the facts recited above constitute either good cause for the arrest of the judgment or an error or impropriety that had a substantial adverse effect on El-dredge’s rights.
Utah Rule of Evidence 702 governs the admissibility of expert opinion testimony. See Utah R.Evid. 702. In Kofford v. Flora, 744 P.2d 1343, 1347 (Utah 1987), this Court held that a foundational showing establishing the reliability of such evidence is required for its admission under rule 702. At a hearing on Eldredge’s post-trial motions, it was shown that Harrison’s doubts were based solely on Eldredge’s failure to confess. This is not a foundation adequate [39]*39to establish the reliability of any opinion as to Eldredge’s guilt that Harrison might give at a new trial. Moreover, there is no reason to believe that any opinion of Harrison’s as to Eldredge’s guilt or innocence would be admissible, even if the foundation were stronger. See, e.g., State v. Rammel. Thus Harrison’s opinion regarding El-dredge’s guilt was inadmissible under rule 702, and the trial court could properly have denied Eldredge’s motion for a new trial or an arrest of judgment on that ground.
We have considered Eldredge’s other claims and find them to be without merit. The convictions are affirmed.
HALL, C.J., and DURHAM, J., concur.