The U.S. Supreme Court ruled Tuesday that states must take into account a margin of error in IQ testing when determining whether or not an individual has intellectual disability. (Shutterstock)

WASHINGTON — A closely divided Supreme Court on Tuesday struck down Florida’s strict IQ cutoff for determining inmate eligibility for the death penalty.

In a 5-4 ruling, the court concluded that the state’s rigid IQ cutoff of 70 “disregards established medical practice” and creates the “unacceptable risk” that an inmate with intellectual disability might be executed in violation of the Constitution.

“Our society does not consider this strict cutoff as proper or humane,” Justice Anthony Kennedy wrote.

Instead, Kennedy and the court’s four liberal justices concluded, Florida must take into account other factors as well as the IQ testing’s standard error of measurement in evaluating intellectual disability. This is already the practice in many other states.

“By failing to take into account the (standard error of measurement) and setting a strict cutoff at 70, Florida goes against the unanimous professional consensus,” Kennedy wrote, adding that “the flaws in Florida’s law are the result of the inherent error in IQ tests themselves. An IQ score is an approximation, not a final and infallible assessment of intellectual functioning.”

Freddie Lee Hall, the 68-year-old convicted murderer at the heart of the case decided Tuesday, has been on the state’s death row since 1978. He and an accomplice were convicted of murdering a 21-year-old pregnant woman and a Hernando County deputy sheriff.

The sixteenth of 17 children, Hall was “tortured by his mother and abused by his neighbors,” according to a 1993 dissenting opinion in the Florida Supreme Court. He had an IQ of 60 and was “functionally illiterate and has the short-term memory of a first-grader,” the dissenting opinion observed. In later years, though, Hall’s IQ was variously measured at 71 and 73.

Hall and Mack Ruffin Jr. were charged in the Feb. 21, 1978 murders of Karol Lea Hurst, a 21-year-old housewife who was seven months pregnant, and Hernando County Deputy Sheriff Lonnie Coburn.

The Supreme Court has previously decided, in a 2002 case called Atkins v. Virginia, that the execution of those variously described as having mental retardation or intellectual disability violates the Eighth Amendment’s prohibition against cruel and unusual punishment. The court left the definition up to individual states.

“No legitimate penological purpose is served by executing a person with intellectual disability,” Kennedy wrote in the decision issued Tuesday. “To do so contravenes the Eighth Amendment, for to impose the harshest of punishments on an intellectually disabled person violates his or her inherent dignity as a human being.”

Florida imposes a three-part test, which starts with a rigid requirement that the inmate score 70 or below on the IQ test. If the inmate scores below the cutoff number, the state also will assess for “deficits in adaptive behavior” and an onset before the age of 18.

In addition to the intelligence test score cutoff, Florida defines intellectual disability as a condition that appears in childhood and is accompanied by “deficits in adaptive behavior,” which essentially means the ability to live independently. By one count, more than a dozen other states use an IQ score of 70 as a cutoff point, giving the Supreme Court’s ultimate ruling potentially more significance.

In the 2002 case, called Atkins v. Virginia, a divided court first concluded that the execution of people with intellectual disability violated the Constitution’s Eighth Amendment protections against cruel and unusual punishment. The court’s 6-3 majority reasoned that “society views mentally retarded offenders as categorically less culpable than the average criminal.”

Conservative Justice Samuel Alito wrote a dissent, joined by Chief Justice John Roberts, Jr., as well as Antonin Scalia and Clarence Thomas.

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