[¶ 1] Mark Osier appeals from a judgment of conviction for engaging in sexual contact with a minor under 15 years of age, in violation of Section 12.1-20-03, N.D.C.C. We hold the trial court’s admission of evidence that Osier engaged in prior incidents of sexual misconduct with a minor constituted revers*442ible error, and we reverse the judgment of conviction and remand for a new trial.
[¶2] The State charged Osier with six separate counts of engaging in sexual intercourse with his daughter, between January and November 1994, when she was under 15 years of age. A jury found Osier guilty on all six counts, and the court sentenced Osier to serve 20 years at the penitentiary on count one and ten years, all suspended, on counts two through six, consecutive to count one. Osier appealed.
Prior Bad Act Testimony
[¶ 3] Osier asserts the trial court committed reversible error by allowing Osier’s niece to testify about prior incidents of Osier sexually fondling her. She testified, over Osier’s objection, that when she was eight or nine years old Osier “put his hands up my shirt,” “kissed me and stuck his tongue in my mouth” and, in another instance, took her from the room she was sleeping in at his home and touched her “between my legs” and then “took me upstairs into his bedroom” and then “had me feel his penis.” The trial court admitted this evidence and instructed the jury it was for the limited purpose “of showing motive scheme or plan with respect to the offense charged.”
[¶ 4] The admission of prior bad act evidence is governed by Rule 404(b), N.D.R.Ev.:
“(b) Other Crimes, Wrongs, or Acts. Evidence of other crimes, wrongs, or acts is not admissible to prove the character of a person in order to show action in conformity therewith. However, it may be admissible for other purposes, such as proof of motive, opportunity, intent, preparation, plan, knowledge, identity, or absence of mistake or accident, provided that the prosecution in a criminal case shall provide reasonable notice in advance of trial, or during trial if the court excuses pretrial notice on good cause shown, of the general nature of any such evidence it intends to introduce at trial.”
Under this rule, evidence of prior bad acts or crimes is generally not admissible “unless it is substantially relevant for some purpose other than to point out the defendant’s criminal character and thus to show the probability that he acted in conformity therewith.” State v. Biby, 366 N.W.2d 460, 463 (N.D.1985). The rule acknowledges the inherent prejudicial effect prior bad act evidence may have on the trier of fact. State v. Micko, 393 N.W.2d 741, 744 (N.D.1986). The rule does not authorize automatic admission merely because the proponent advances a proper purpose for the evidence; instead, the relevance and probative value of the evidence must be demonstrated. Dahlen v. Landis, 314 N.W.2d 63, 70 (N.D.1981).
[¶ 5] The State invoked the entire litany of exceptions listed under Rule 404(b), N.D.R.Ev., for admitting the niece’s testimony.1 It failed, however, to specifically articulate how Osier’s inappropriate sexual touching of his niece eight years prior to the alleged acts of intercourse with his daughter was relevant to any material-issue or for any admissible purpose under Rule 404(b), N.D.R.Ev. We can glean no purpose for this evidence from the facts in this case other than to show that if Osier sexually assaulted a niece eight years ago to satisfy some lust, desire, or need for sexual contact with a young girl, then it is probable he satisfied the same lust, desire, or need eight years later by having intercourse with his minor daughter. That use of the niece’s testimony is nothing more than propensity evidence to show Osier had a criminal sexual character and, in all probability, he acted in conformity therewith in committing the charged acts of *443intercourse. Rule 404(b), N.D.R.Ev., prohibits such use of this evidence.
[¶ 6] In similar circumstances, we have warned of the dangers of opening the door to this type of propensity evidence and of tempting a jury to convict a defendant for his past actions rather than on evidence of the charged misconduct. State v. Forsland, 326 N.W.2d 688, 693 (N.D.1982); State v. Flath, 61 N.D. 342, 237 N.W. 792, 794 (1931); see also State v. Micko, 393 N.W.2d at 745; State v. Stevens, 238 N.W.2d 251, 258 (N.D.1975), overruled on other grounds, State v. Himmerick, 499 N.W.2d 568, 572 (N.D.1993) [plea of not guilty in a criminal bench trial ease preserves for appeal the issue of sufficiency of the evidence].
[¶ 7] Our decisions in Forsland and Flath are particularly relevant to the factual circumstances of this case and provide instructive guidance on the issue of the admissibility of the niece’s testimony. The defendant in Flath was convicted for “taking indecent liberty” with a young boy. The defendant had been charged in two separate cases of committing similar acts with two other boys. At trial, those boys testified about the defendant’s prior acts of sexual misconduct with them. We held admission of that testimony constituted reversible error, stating:
‘We are entirely at a loss to see any legal basis in this case for the admission of the evidence relating to the alleged other offenses. The real purpose for the introduction thereof seems to have been that stated by the prosecuting attorney, namely, to show ‘the general licentious character of the defendant’; and it is settled beyond question that the state may not adduce evidence of other crimes for this purpose.
“ ‘In a criminal ease the prosecution may not introduce evidence tending to prove that the defendant was morally deficient, that he possessed a criminal disposition generally, or that he was particularly disposed to commit the offense with which he is charged, and, to this end, it may not introduce evidence of the defendant’s participation in other acts which are criminal or which involve moral turpitude.... ’
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“The acts committed upon one boy were in no sense part of the res gestae as regards the criminal conduct towards another. There is no question as to the identity of the person who committed the crime charged in this case. If the crime was committed, it was committed by the defendant and no one else. There is no question as to motive or intent; there is no claim and no basis for a claim that the particular criminal acts alleged to have been committed in this case might have been accidental or innocent. As was said by the Supreme Court of the state of Michigan, in a ease involving a somewhat similar charge: ‘The question of defendant’s “motive, intent, the absence of, mistake or accident on his part” is clearly not involved in the charge as laid. Neither do we think that it can be said that in the commission of the crime charged he was acting in conformity with any “scheme” or “plan” theretofore formulated by him, or that proofs of similar acts with others in any way tend to inform the court or jury as to his “system” in doing the act complained of.’ People v. Dean, 253 Mich. 434, 235 N.W. 211, 212....
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We are agreed that the trial court erred in admitting the evidence relating to the alleged criminal acts upon the two other boys.”
State v. Flath, 237 N.W. at 793-794. Here, too, there is no permissible basis for admitting testimony about Osier’s prior sexual misconduct. The State did not demonstrate an operative scheme or plan common to Osier’s alleged sexual fondling of his niece and his charged acts of unlawful intercourse with his daughter to justify admitting the prior acts evidence.
[¶ 8] Admission of the niece’s testimony to show motive, also cannot withstand scrutiny under Rule 404(b), N.D.R.Ev. To say that Osier’s sexual fondling of his niece is probative of his motive eight years later in having sexual intercourse with his daughter is nothing more than a veiled offer of propensity evidence. Candidly stated, the only relevance of the niece’s testimony to motive is to *444demonstrate Osier presumably had an unseemly motive (e.g., improper lust, desire, or need) for sexually assaulting his niece and therefore he presumably must also have acted with the same motive in committing the charged acts of intercourse with his daughter. That is precisely the use of prior bad act testimony prohibited by this court in Flath and again rejected by this court in State v. Forsland.
[¶ 9] The defendant in Forsland was convicted of indecent exposure and sexual assault. After the victim completed her night shift at a Fargo hospital, she crossed the street from the hospital and entered a parking ramp where her car was parked. As she opened the car door, a man reached into the car, grabbed her in the crotch area, and exposed himself. At trial, the prosecution introduced evidence that two months prior to the charged incident the defendant exposed himself at the same parking ramp. This court held the evidence was inadmissible under Rule 404(b), N.D.R.Ev., and, citing approvingly to an Iowa Law Review article, cautioned about the dangers underlying the trend of allowing prior crime evidence in sexual assault cases:
“In volume 41, Iowa Law Review (1956), page 333, entitled Other Vices, Other Crimes, the use or non-use of prior offenses is discussed, and the author makes some interesting statements:
“ ‘[The] possibility is high that the jury will convict on the basis of character alone, and prejudice dictates the decisions of the triers of fact.
“ “Yet courts have lost all feeling for tradition and the meaning of prejudice when applying rules of exclusion in prosecutions for sex offenses. A strong line of authorities today holds that evidence of other crimes is admissible for the purpose of showing a degenerate disposition, a lustful disposition, or an inclination to commit sexual offenses.’
“The eases relied upon by the author are not all of recent vintage. The article continues:
“ ‘When deciding the issue of guilt or innocence in sex cases, where prejudice has reached its loftiest peak, our courts have been most liberal in announcing and fostering a nebulous exception, offering scant attention to inherent possibilities of prejudice. Just when protection is most needed, the rules collapse.’ ⅜ * * * *
“[W]e conclude that the evidence pertaining to the admission of the defendant’s prior plea of guilty on a similar offense could not be used in determining whether or not the defendant was guilty or innocent of the crime charged.”
State v. Forsland, 326 N.W.2d at 693.
[¶ 10] Our analysis and conclusions in Flath and Forsland are determinative here. There is no permissible basis under the circumstances of this case for admitting the niece’s testimony under Rule 404(b), N.D.R.Ev. Her testimony was not relevant to a genuine issue regarding motive, scheme, plan, or any other listed exception under Rule 404(b), N.D.R.Ev. The sole purpose served by her testimony was to demonstrate Osier’s criminal sexual character to show he probably acted in conformity with that character in committing • the acts charged. As this court stated in State v. Stevens, 238 N.W.2d 251, 257 (N.D.1975), “in the final analysis, the question before the court, trial or appellate, is one of balancing the aims of full disclosure and fairness to the defendant where they are in conflict. The basic question is fundamental, fairness.” It is fundamentally unfair to tempt a jury to convict a defendant circumstantially on the basis of prior misconduct or character propensity rather than upon evidence of the criminal acts charged. We conclude the trial court erred in admitting the niece’s testimony.
Harmless Error Review
[¶ 11] Our review of trial court error is guided by Rule 52(a), N.D.R.Crim.P.:
“(a) Harmless Error. Any error, defect, irregularity or variance which does not affect substantial rights shall be disregarded.”
Trial court error which does not prejudice substantial rights of the accused may be disregarded. State v. Micko, 393 N.W.2d at 746. [¶ 12] Osier’s daughter testified that on *445numerous occasions during 1994, when she was 13 or 14 years old, her father forced her to have sexual intercourse with him when her mother was away on business trips. Dr. Ron Miller, a pediatric physician practicing in Fargo, examined Osier’s daughter. He concluded she has had sexual intercourse on multiple occasions. There was evidence a young man and acquaintance of Osier’s daughter had one incident of intercourse with her, but Dr. Miller testified a single act of intercourse would not, in his opinion, have caused her physical condition. Osier’s niece then testified Osier sexually molested her on several occasions when she was eight or nine years old.
[¶ 13] Although corroborated by Dr. Miller’s testimony, the primary evidence against Osier is his daughter’s testimony, and her credibility is therefore crucial to the State’s case. Under these circumstances, the niece’s testimony about Osier sexually molesting her is highly prejudicial and could have affected the jury’s determination. The jury could have decided to believe the daughter’s assertion Osier molested her because Osier previously molested his niece. In this regard, the admission of Osier’s prior conduct of molesting his niece is similar- to the admission of prior crime evidence in State v. Forsland, 326 N.W.2d at 694, which this court held to be reversible error. See also State v. Ferguson, 391 N.W.2d 172,175 (N.D. 1986) (admission of prior conviction of gross sexual imposition in defendant’s trial for terrorizing necessitated reversal and remand for new trial because of “the possible prejudice resulting from admission of this highly prejudicial evidence”). After reviewing the record in this case, we conclude the jury may have reached a different decision absent the erroneous admission of the niece’s prior bad conduct testimony.
[¶ 14] Other issues raised by Osier need not be addressed, because they are not necessary to disposition of this appeal and do not involve matters likely to recur during the retrial. Questions, the answers to which are not necessary to the determination of an appeal, need not be considered. City of Fargo v. Ness, 529 N.W.2d 572, 577 (N.D.1995).
[¶ 15] The judgment of conviction is reversed and the case is remanded for a new trial.
[¶ 16] VANDE WALLE,C,J., and MARING and MESCHKE, JJ., concur.. The State argues on appeal, this court should "adopt the standards adopted by the Federal Rules” which Congress enacted in 1994 for admitting prior bad act evidence in cases- involving sexual assault or child molestation. Rule 414, Fed.R.Ev., provides in relevant part:
"(a) In a criminal case in which the defendant is accused of an offense of child molestation, evidence of the defendant's commission of another offense or offenses of child molestation is admissible, and may be considered for its bearing on any matter to which it is relevant.”
We decline the State’s invitation to consider this rule. We have a formal process for adopting procedural rules, utilizing the Joint Procedure Committee, a standing committee of this court, chaired by Justice Dale V. Sandstrom. We do not adopt procedural rules by opinion in litigated appeals.