The two-justice dissent continued in relevant part: Because these courts have defined intellectual disability for capital cases in direct reference to the medical consensus, it is far from clear that Coonce would be denied an Atkins hearing in these five States (totaling 41) solely because his impairments fully manifested at age 20. See Moore, 581 U. S., at ___, ___ (slip op., at 8, 17) (holding that “adherence to superseded medical standards,” as opposed to reliance on “current manuals which offer the best available description of how mental disorders are expressed and can be recognized by trained clinicians,” violated the Eighth Amendment (internal quotation marks omitted)). Only nine States with capital punishment have adopted a statutory age-18 onset requirement for Atkins claims. See Ariz. Rev. Stat. Ann. §13–753(K)(3) (2020); Ark. Code Ann. §5–4–618(a)(1)(A) (Supp. 2021); Fla. Stat. §921.137(1) (2015); Idaho Code Ann. §19–2515A(1)(a) (2017); Mo. Rev. Stat. §565.030(6) (2016); N. C. Gen. Stat. Ann. §15A–2005(a)(1) (2019); Okla. Stat., Tit. 21, §701.10b(B) (Supp. 2020); S. D. Codified Laws §23A–27A–26.1 (Cum. Supp. 2019); Tenn. Code Ann. §39–13–203(a)(3) (Supp. 2021). There is no reason to assume that on reconsideration, the Eighth Circuit would necessarily side with this minority of jurisdictions.
Three of these States (California, Colorado, and Virginia) enacted these reforms just during the pendency of Coonce’s petition for certiorari. On the whole, there is “strong evidence of consensus that our society does not regard this strict cutoff as proper or humane.” Hall, 572 U. S., at 718. As the Government concedes, with the new information, there is at least “a reasonable probability” the Eighth Circuit would conclude that Coonce has demonstrated timely onset of his impairments. Brief in Opposition 13 (internal quotation marks omitted).
The Government also tells us that a redetermination by the Eighth Circuit “may determine the ultimate outcome” of Coonce’s Atkins claim. Brief in Opposition 13 (internal quotation marks omitted). Indeed, even without a hearing, Coonce has produced convincing evidence on the first two prongs of intellectual disability. A defense psychologist who reviewed documentary evidence and administered a comprehensive battery of tests on Coonce across two 4-hour sessions determined that he had an IQ of 71, within the accepted range for intellectual disability. See Moore, 581 U. S., at ___ (IQ score of 74, accounting for standard error, required consideration of adaptive functioning); Brumfield v. Cain, 576 U. S. 305, 315 (2015) (state court unreasonably applied Hall in finding IQ score of 75 to preclude intellectual disability); Hall, 572 U. S., at 712–714 (if IQ score is close to 70, courts must account for “standard error of measurement”). Coonce therefore has put forth evidence to establish that he has “significantly subaverage intellectual functioning.” Id., at 710.
The setting of a firm IQ number of 70 is arbitrary on the one hand. Many of the reasons that support the use of this round number would also apply to a 69 and 71 IQ. On the other hand, if a firm number is not set, it invites inconsistent and arbitrary results.