In 2002, the U.S. Supreme Court determined that the prohibition against cruel and unusual punishment prevents governments from executing intellectually disabled defendants. (The court formerly used the phrase “mentally retarded.”) (Atkins v. Virginia, 536 U.S. 304 (2002).) The Court left it to the states to establish procedures by which courts determine intellectual disability.
(To read about the rationale for prohibiting capital punishment for the intellecutally disabled, see Supreme Court Makes it Harder to Execute the Intellectually Disabled.)
In 2014, the Supreme Court struck down a Florida law that made defendants with IQ scores higher than 70 eligible for death. (Hall v. Florida, 572 U.S. ____ (2014).) According to the law, if a defendant scored a 71 on an IQ test, he could be executed and couldn’t present any evidence to try to persuade the court of intellectual disability.
The Supreme Court found Florida’s law unconstitutional, noting that the overwhelming majority of states didn’t take this approach. It also observed that IQ is an imprecise measurement, such that someone who scores a 71 could very well have an IQ of anywhere from 66 to 76. Further, it reasoned that people can be intellectually disabled even if they have IQs over 70.
The Court’s 2014 holding means that states can’t use a 70 IQ score as a bright line for death-penalty eligibility. When an IQ score falls within the test’s margin of error, the defense must be able to present other evidence of intellectual disability. That means that, if 70 is the cutoff point, with a margin of error of five, a defendant who scores between 70 and 75 must have the chance to offer additional evidence.