Because “intellectual disability is a condition, not a number,” and an IQ score is an approximation, not a final and infallible assessment of intellectual functioning, the Supreme Court invalidates Florida’s bright-line rule that a defendant is not intellectually disabled—and thus may be executed—if he has never scored below 70 on an IQ test.
Atkins v. Virginia, 536 U.S. 304 (2002), held that the Eighth Amendment prohibits the execution of a person who is found to be “intellectually disabled” (the phrase replaces “mentally retarded” (slip op. at 2)). But beyond noting the broad outline of the clinical definitions of the phrase—”significantly subaverage intellectual functioning” along with “significant limitations in adaptive skills such as communication, self-care, and self-direction that become manifest before age 18”—the Court left it to the states to implement and further define the appropriate standard. 536 U.S. at 317-18.
Some states specify that “significantly subaverage intellectual functioning” is determined using an IQ cutoff score, so that a defendant whose IQ test results never fall below that score doesn’t meet the definition and is thus eligible for execution. Florida is one of those states, as its statutes refers to a test score “two or more standard deviations from the mean score on a standardized intelligence test,” Fla. Stat. § 921.137(1). While that statute seemingly leaves room for taking account of the margin of error in measurement, and expressing a test result as a range of scores around a single result rather than a single number, Florida courts rejected that reading of the statute. Thus, under Florida law the score cutoff was a rigid 70. (Slip op. at 9). Hall’s test results were between 71 and 80, but never below 70, so he couldn’t meet the definition of intellectually disabled. (Slip op. at 4-5, 8-9).
The Supreme Court now holds that this “rigid rule … creates an unacceptable risk that persons with intellectual disability will be executed, and thus is unconstitutional.” (Slip op. at 1). Citing the “evolving standards of decency” test applied to Eighth Amendment claims, Trop v. Dulles, 356 U.S. 86, 101 (1958) (plurality opinion), the Court considers the professional medical communities approach to intellectual disability, the approaches taken by other states, and its own independent judgment. (Slip op. at 5-7).
A mandatory score cutoff is inconsistent with the professional consensus about how to determine intellectual disability because it takes an IQ score as final and conclusive evidence of a defendant’s intellectual capacity, when experts in the field would consider other “substantial and weighty” evidence of intellectual disability, including medical histories, behavioral records, school tests and reports, and testimony regarding past behavior and family circumstances. Florida’s rigid rule also relies on a purportedly scientific measurement of a defendant’s abilities without recognizing that the score is, on its own terms, imprecise. (Slip op. at 7-12). By contrast, only a few death penalty states mandate a strict score cutoff; most take the standard error of measurement into account or allow the consideration of other evidence even when the defendant has a score above the cutoff. (Slip op. at 12-16). This is “strong evidence of consensus that our society does not regard this strict cutoff as proper or humane.” (Slip op. at 16). The professional consensus and the approach taken by most states in turn support the Court’s independent judgment that “[i]ntellectual disability is a condition, not a number,” and therefore “[i]t is not sound to view a single factor as dispositive of a conjunctive and interrelated assessment.” (Slip op. at 21).
Justice Alito dissents, joined by the Chief Justice and Justices Scalia and Thomas, criticizing the majority opinion at length as “based largely on the positions adopted by private professional associations” and “adopt[ing] a uniform national rule that is both conceptually unsound and likely to result in confusion.” (Dissent at 1).
This decision has no direct bearing on state practice, of course, though the majority opinion’s discussion may provide ammunition in a case where an intellectually disabled defendant’s competency is at issue and the state or the court are relying heavily, or even exclusively, on a single IQ test result.