In Clark v. Arizona, 548 U.S. 735 (2006), the Court considered the three different categories of evidence "with a potential bearing" on the mental state element of an offense: observation, mental disease, and mental capacity. "Observation evidence" includes lay and expert testimony "from those who observed what a defendant did and heard what he said." It includes testimony of an expert witness about a defendant's "tendency to think in a certain way and his behavioral characteristics." "Mental-disease evidence" consists of opinions that the defendant "suffers from a mental disease with features described by the witness." And "capacity evidence" is evidence of a defendant's "ability to form a certain state of mind or motive, understand or evaluate one's actions, or control them.". The Court held observation evidence, even from an expert, is admissible to show a defendant did not have the requisite mental state to commit the charged offense. Id. at, 126 S. Ct. at 2726. The United States Supreme Court observed that there is a vigorous debate within the profession about the contours of mental disease. (when considering constitutionality of state evidentiary rule excluding diminished capacity evidence in all but NGI cases.) Additional concerns identified by the court are the controversial character of some categories of mental disease and the potential of mental-disease evidence to mislead. (Ibid.) Although McFadden claims the elimination of her defense violated constitutional guarantees of due process and fundamental fairness, the decision in Clark defeats her argument. The court held that a state may choose to limit the evidence of mental illness in an NGI trial. The defendant in Clark alleged that evidence of his mental illness should have been considered to show he did not at the time of the offense have the knowledge or intent to shoot a police officer, in other words, a specific mental-state element. (Id. at p. 788.) In Arizona, under the law at the time Clark was decided, even mental health evidence defeating specific-intent mens rea was limited to NGI trials. The court stated: "'While the Constitution ... prohibits the exclusion of defense evidence under rules that serve no legitimate purpose or that are disproportionate to the ends that they are asserted to promote, well-established rules of evidence permit trial judges to exclude evidence if its probative value is outweighed by certain other factors such as unfair prejudice, confusion of the issues, or potential to mislead the jury.' . And if evidence may be kept out entirely, its consideration may be subject to limitation, which Arizona claims the power to impose here. State law says that evidence of mental disease and incapacity may be introduced and considered, and if sufficiently forceful to satisfy the defendant's burden of proof under the insanity rule it will displace the presumption of sanity and excuse from criminal responsibility. But mental-disease and capacity evidence may be considered only for its bearing on the insanity defense, and it will avail a defendant only if it is persuasive enough to satisfy the defendant's burden as defined by the terms of that defense. The mental-disease and capacity evidence is thus being channeled or restricted to one issue and given effect only if the defendant carries the burden to convince the factfinder of insanity; the evidence is not being excluded entirely, and the question is whether reasons for requiring it to be channeled and restricted are good enough to satisfy the standard of fundamental fairness that due process requires. We think they are." (Clark v. Arizona, supra, 548 U.S. at pp. 770-771.)