The Supreme Court has ruled that the death penalty is not a per se violation of the Eighth Amendment’s ban on “cruel and unusual punishments,” but it has interpreted the Eighth Amendment to require that the death penalty be applied with reasonable consistency while at the same time accounting for individual fairness. Furthermore, because the Eighth Amendment requires that penalties be proportionate to the crime punished, certain crimes are not eligible for the death penalty. Similarly, certain defendants may not be executed. In 2002, the Court ruled in Atkins v. Virginia that executing mentally disabled criminals violates the ban on cruel and unusual punishments because their mental handicap lessens the severity of the crime, rendering the extraordinary penalty of death disproportionately severe.
This term, in Hall v. Florida, the Court examined Florida’s IQ threshold, which set a bright-line cutoff at 70 IQ for death-penalty eligibility. In that case, petitioner Hall had asked a Florida state court to vacate his prior death sentence, presenting evidence that included an IQ test score of 71. The court denied his motion, determining that a Florida statute mandated that he show an IQ score of 70 or below before being permitted to present any additional evidence of intellectual disability. The Florida Supreme Court rejected Hall’s appeal, finding the State’s 70-point threshold constitutional.
In a 5–4 decision by Justice Kennedy, the Court struck down Florida’s 70-point threshold under the Eighth Amendment. In considering whether the threshold complied with the rule announced with Atkins, the Court considered the psychiatric and professional studies that elaborate on the purpose and meaning of IQ scores as well as how the states have implemented Atkins. According to the majority, Florida’s rule failed on both fronts. First, the Court identified two ways in which Florida’s rule disregarded established medical practice: It took an IQ score as final and conclusive evidence of a defendant’s intellectual capacity, when experts would consider other evidence; and it relied on a purportedly scientific measurement of a defendant’s abilities, while refusing to recognize that measurement’s inherent imprecision. Second, the Court noted that the vast majority of states have rejected bright-line IQ cutoffs for the purposes of imposing the death penalty. The Court concluded, based on consensus of the medical and psychiatric community as well as the consensus of the states, that a defendant must be able to present additional evidence of intellectual disability when the defendant’s IQ test score falls within the test’s acknowledged and inherent margin of error.
Justice Alito, joined by Chief Justice Roberts and Justices Scalia and Thomas, dissented. According to Justice Alito, Atkins left the determination of mental competency to the states, explicitly declining to adopt a national standard. Justice Alito dissented from both what he saw as the majority’s implicit adoption of just such a standard, as well as the standard itself.
As a result of this decision, states may still consider IQ tests and even have IQ thresholds in the death penalty context, but IQ alone cannot serve as the final and conclusive evidence of a defendant’s intellectual capacity. Defendants must be allowed to present other evidence of intellectual disability, such as testimony regarding adaptive deficits, whenever a defendant’s IQ test results fall within the test’s margin of error.