Cite as: 509 U. S. 312 (1993)
Opinion of the Court
record. Finally, courts are compelled under rational-basis review to accept a legislature's generalizations even when there is an imperfect fit between means and ends. A classification does not fail rational-basis review because it " 'is not made with mathematical nicety or because in practice it results in some inequality.' " Dandridge v. Williams, supra, at 485, quoting Lindsley v. Natural Carbonic Gas Co., 220 U. S. 61, 78 (1911). "The problems of government are practical ones and may justify, if they do not require, rough accommodations—illogical, it may be, and unscientific." Metropolis Theatre Co. v. Chicago, 228 U. S. 61, 69-70 (1913). See also, e. g., Burlington Northern R. Co. v. Ford, 504 U. S. 648, 651 (1992); Vance v. Bradley, supra, at 108, and n. 26; New Orleans v. Dukes, supra, at 303; Schweiker v. Wilson, 450 U. S. 221, 234 (1981). We have applied rational-basis review in previous cases involving the mentally retarded and the mentally ill. See Cleburne v. Cle-burne Living Center, Inc., 473 U. S. 432 (1985); Schweiker v. Wilson, supra. In neither case did we purport to apply a different standard of rational-basis review from that just described.
True, even the standard of rationality as we so often have defined it must find some footing in the realities of the subject addressed by the legislation. That requirement is satisfied here. Kentucky has proffered more than adequate justifications for the differences in treatment between the mentally retarded and the mentally ill.
A
Kentucky argues that a lower standard of proof in commitments for mental retardation follows from the fact that mental retardation is easier to diagnose than is mental illness. That general proposition should cause little surprise, for mental retardation is a developmental disability that becomes apparent before adulthood. See American Psychiatric Assn., Diagnostic and Statistical Manual of Mental Dis-
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