Courts reviewing whether a death-sentenced defendant is intellectually disabled under Atkins must use current medical standards in considering the claim, the U.S. Supreme Court ruled March 28 in Moore v. Texas.
Bobby James Moore was originally convicted of capital murder and sentenced to death in Texas in 1980.  After that sentence was set aside for ineffective counsel, he ultimately was resentenced to death in 2001.
He sought state habeas relief under Atkins v. Virginia, 536 U.S. 304 (2002), on grounds that he was ineligible for the death penalty since he was intellectually disabled.
The Texas Court of Criminal Appeals ultimately denied relief.  The court relied on intellectual-disability guides from 1992, and Texas case law based “factors” not tied to current medical standards. 
The U.S. Supreme Court reversed, in a 5-3 opinion, but effectively joined by all justices on the issue of whether modern medical standards must be used.
While Atkins expressly left to the States “the task of developing appropriate ways to enforce the restriction on executing the intellectually disabled,” the Court said, that discretion “is not unfettered.” 
“The medical community’s current standards supply one constraint on States’ leeway in this area,” the Court held.
“Even if the views of medical experts do not dictate a court’s intellectual-disability determination … the determination must be informed by the medical community’s diagnostic framework,” the Court said. 
The Texas court improperly relied on outdated medical standards from 1992 in considering whether Moore was intellectually disabled, and also state case law based “factors” that were not tied to current medical standards.
The Texas court failed to consider the standard error of measurement in IQ scores, and deviated from current medical standards in assessing adaptive functioning.  It erroneously found that school problems and child abuse made intellectual disability less likely, even though medical standards regard these as “risk factors for intellectual disability.”  And it improperly required Moore to show that his adaptive deficits were not related to a “personality disorder,” even though the medical community recognizes that the existence of a personality disorder does not mean that a person does not also have intellectual disability.
The Supreme Court noted that the case law based “factors” which Texas used to deny relief were an “outlier” both compared to other States’ handling of intellectual disability claims, and to Texas’ own practice in other contexts.  Texas, for example, mandates that intellectual-disability diagnoses of juveniles be based on “the latest edition of DSM.”
“Texas cannot satisfactorily explain why it applies current medical standards for diagnosing intellectual disability in other contexts, yet clings to superseded standards when an individual’s life is at stake,” the Court concluded.
Even dissenters recognize current medical standards must be used
Chief Justice Roberts, joined by Justices Thomas and Alito, dissented, but “agree[d] with the Court today” that Texas’ use of case law based “factors” not tied to current medical standards “are an unacceptable method of enforcing the guarantee of Atkins.”
Roberts believed that Texas had improperly used its case law based “factors” in considering Moore’s adaptive deficits, but – unlike the majority opinion – Roberts believed Texas had properly considered Moore’s IQ.  He would affirm on that basis.
Roberts’ “broader concern” with the majority’s opinion was that it “abandons the usual mode of analysis this Court has employed in Eighth Amendment cases.” 
The majority overturned the Texas court without considering “objective indicia of society’s standards reflected in the practices among the States,” Roberts said.  “The Court instead crafts a constitutional holding based solely on what it deems to be medical consensus about intellectual disability.”