318
Opinion of Kennedy, J.
Justice Kennedy, with whom Justice O'Connor, Justice Ginsburg, and Justice Breyer join, concurring in part and concurring in the judgment.
I join Parts I, II-A, and II-D of the opinion of the Court. In my view it should have been sufficient to decide this case to observe, as the principal opinion does, that various courts and jurisdictions "may reasonably reach differing conclusions as to whether polygraph evidence should be admitted." Ante, at 312. The continuing, good-faith disagreement among experts and courts on the subject of poly-graph reliability counsels against our invalidating a per se exclusion of polygraph results or of the fact an accused has taken or refused to take a polygraph examination. If we were to accept respondent's position, of course, our holding would bind state courts, as well as military and federal courts. Given the ongoing debate about polygraphs, I agree the rule of exclusion is not so arbitrary or disproportionate that it is unconstitutional.
I doubt, though, that the rule of per se exclusion is wise, and some later case might present a more compelling case for introduction of the testimony than this one does. Though the considerable discretion given to the trial court in admitting or excluding scientific evidence is not a constitutional mandate, see Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U. S. 579, 587 (1993), there is some tension between that rule and our holding today. And, as Justice Stevens points out, there is much inconsistency between the Government's extensive use of polygraphs to make vital security determinations and the argument it makes here, stressing the inaccuracy of these tests.
With all respect, moreover, it seems the principal opinion overreaches when it rests its holding on the additional ground that the jury's role in making credibility determinations is diminished when it hears polygraph evidence. I am in substantial agreement with Justice Stevens' observation that the argument demeans and mistakes the role and
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