(Slip Opinion)
`
`
`
` OCTOBER TERM, 2013
`
`
`Syllabus
`
`1
`
` NOTE: Where it is feasible, a syllabus (headnote) will be released, as is
`
`
`
` being done in connection with this case, at the time the opinion is issued.
`
`
`
` The syllabus constitutes no part of the opinion of the Court but has been
`
` prepared by the Reporter of Decisions for the convenience of the reader.
`
` See United States v. Detroit Timber & Lumber Co., 200 U. S. 321, 337.
`
`
`SUPREME COURT OF THE UNITED STATES
`
`
`
` Syllabus
`
` HALL v. FLORIDA
`
`
`CERTIORARI TO THE SUPREME COURT OF FLORIDA
`
` No. 12–10882. Argued March 3, 2014 —Decided May 27, 2014
`
`After this Court held that the Eighth and Fourteenth Amendments
`
`forbid the execution of persons with intellectual disability, see Atkins
`v. Virginia, 536 U. S. 304, 321, Hall asked a Florida state court to va-
`
`cate his sentence, presenting evidence that included an IQ test score
`of 71. The court denied his motion, determining that a Florida stat-
`ute mandated that he show an IQ score of 70 or below before being
`permitted to present any additional intellectual disability evidence.
`
`The State Supreme Court rejected Hall’s appeal, finding the State’s
`70-point threshold constitutional.
`Held: The State’s threshold requirement, as interpreted by the Florida
`
`Supreme Court, is unconstitutional. Pp. 5–22.
`
`(a) The Eighth Amendment, which “reaffirms the duty of the gov-
`
`
`ernment to respect the dignity of all persons,” Roper v. Simmons, 543
`
`U. S. 551, 560, prohibits the execution of persons with intellectual
`disability. No legitimate penological purpose is served by executing
`
`
`the intellectually disabled. Atkins, 563 U. S., at 317, 320. Prohibit-
`ing such executions also protects the integrity of the trial process for
`individuals who face “a special risk of wrongful execution” because
`they are more likely to give false confessions, are often poor witness-
`
`
`es, and are less able to give meaningful assistance to their counsel.
`
`
`Id., at 320–321. In determining whether Florida’s intellectual disa-
`bility definition implements these principles and Atkins’ holding, it is
`proper to consider the psychiatric and professional studies that elab-
`orate on the purpose and meaning of IQ scores and how the scores re-
`late to Atkins, and to consider how the several States have imple-
`mented Atkins. Pp. 5–7.
`
`(b) Florida’s rule disregards established medical practice. On its
`face, Florida’s statute could be consistent with the views of the medi-
`
`
`cal community discussed in Atkins and with the conclusions reached
`
`
`
`
`
`
`
`
`
`
`
`

`
`HALL v. FLORIDA
`
`
`Syllabus
`
`here. It defines intellectual disability as the existence of concurrent
`
`deficits in intellectual and adaptive functioning, long the defining
`
`characteristic of intellectual disability. See Atkins, supra, at 308.
`
`And nothing in the statute precludes Florida from considering an IQ
`
`test’s standard error of measurement (SEM), a statistical fact reflect-
`
`
`ing the test’s inherent imprecision and acknowledging that an indi-
`vidual score is best understood as a range, e.g., five points on either
`side of the recorded score. As interpreted by the Florida Supreme
`Court, however, Florida’s rule disregards established medical prac-
`tice in two interrelated ways: It takes an IQ score as final and con-
`clusive evidence of a defendant’s intellectual capacity, when experts
`would consider other evidence; and it relies on a purportedly scien-
`tific measurement of a defendant’s abilities, while refusing to recog-
`nize that measurement’s inherent imprecision. While professionals
`have long agreed that IQ test scores should be read as a range, Flori-
`
`da uses the test score as a fixed number, thus barring further consid-
`eration of other relevant evidence, e.g., deficits in adaptive function-
`ing, including evidence of past performance, environment, and
`
`upbringing. Pp. 7–12.
`
`
`
`(c) The rejection of a strict 70-point cutoff in the vast majority of
`
`States and a “consistency in the trend,” Roper, supra, at 567, toward
`recognizing the SEM provide strong evidence of consensus that socie-
`
`ty does not regard this strict cutoff as proper or humane. At most,
`nine States mandate a strict IQ score cutoff at 70. Thus, in 41
`States, an individual in Hall’s position would not be deemed automat-
`ically eligible for the death penalty. The direction of change has been
`
`consistent. Since Atkins, many States have passed legislation to
`comply with the constitutional requirement that persons with intel-
`lectual disability not be executed. Two of those States appear to set a
`strict cutoff at 70, but at least 11 others have either abolished the
`death penalty or passed legislation allowing defendants to present
`additional intellectual disability evidence when their IQ score is
`above 70. Every state legislature, save one, to have considered the
`
`issue after Atkins and whose law has been interpreted by its courts
`has taken a position contrary to Florida’s. Pp. 12–16.
`(d) Atkins acknowledges the inherent error in IQ testing and pro-
`
`vides substantial guidance on the definition of intellectual disability.
`The States play a critical role in advancing the protections of Atkins
`
`and providing this Court with an understanding of how intellectual
`
`disability should be measured and assessed, but Atkins did not give
`
`them unfettered discretion to define the full scope of the constitution-
`al protection. Clinical definitions for intellectual disability which, by
`their express terms, rejected a strict IQ test score cutoff at 70, and
`which have long included the SEM, were a fundamental premise of
`
`
`
`
`
`
`
`2
`
`
`
`
`

`
`
`
` Cite as: 572 U. S. ____ (2014)
`
`
`Syllabus
`Atkins. See 536 U. S., at 309, nn. 3, 5. A fleeting mention of Florida
`in a citation listing States that had outlawed the execution of the in-
`tellectually disabled, id., at 315, did not signal the Atkins Court’s ap-
`proval of the State’s current understanding of its law, which had not
`yet been interpreted by the Florida Supreme Court to require a strict
`
`70-point cutoff. Pp. 16–19.
`(e) When a defendant’s IQ test score falls within the test’s
`
`acknowledged and inherent margin of error, the defendant must be
`able to present additional evidence of intellectual disability, including
`testimony regarding adaptive deficits. This legal determination of in-
`tellectual disability is distinct from a medical diagnosis but is in-
`formed by the medical community’s diagnostic framework, which is of
`particular help here, where no alternative intellectual disability defi-
`nition is presented, and where this Court and the States have placed
`
`substantial reliance on the medical profession’s expertise. Pp. 19–22.
`109 So. 3d 704, reversed and remanded.
`KENNEDY, J., delivered the opinion of the Court, in which GINSBURG,
`
`
`BREYER, SOTOMAYOR, and KAGAN, JJ., joined. ALITO, J., filed a dissent-
`
`
`
`
`
` ing opinion, in which ROBERTS, C. J., and SCALIA and THOMAS, JJ.,
`
`
`
`
`joined.
`
`
`
`
`
`3
`
`
`
`
`
`

`
`
`
`
`
` Cite as: 572 U. S. ____ (2014)
`
`Opinion of the Court
`
`1
`
`
` NOTICE: This opinion is subject to formal revision before publication in the
`
`
`
` preliminary print of the United States Reports. Readers are requested to
`
` notify the Reporter of Decisions, Supreme Court of the United States, Wash­
`
` ington, D. C. 20543, of any typographical or other formal errors, in order
`
`
` that corrections may be made before the preliminary print goes to press.
`
`
`
`
`SUPREME COURT OF THE UNITED STATES
`
`
`
`_________________
` No. 12–10882
`_________________
`
` FREDDIE LEE HALL, PETITIONER v. FLORIDA
`ON WRIT OF CERTIORARI TO THE SUPREME COURT OF
`
`
`FLORIDA
`
`[May 27, 2014]
`
`JUSTICE KENNEDY delivered the opinion of the Court.
`This Court has held that the Eighth and Fourteenth
`
`
`Amendments to the Constitution forbid the execution of
`persons with intellectual disability. Atkins v. Virginia,
`536 U. S. 304, 321 (2002). Florida law defines intellectual
`disability to require an IQ test score of 70 or less. If, from
`
`test scores, a prisoner is deemed to have an IQ above 70,
`all further exploration of intellectual disability is fore­
`closed. This rigid rule, the Court now holds, creates an
`unacceptable risk that persons with intellectual disability
`
`will be executed, and thus is unconstitutional.
`I
`
`On February 21, 1978, Freddie Lee Hall, petitioner here,
`and his accomplice, Mark Ruffin, kidnaped, beat, raped,
`and murdered Karol Hurst, a pregnant, 21-year-old new­
`lywed. Afterward, Hall and Ruffin drove to a convenience
`store they planned to rob. In the parking lot of the store,
`they killed Lonnie Coburn, a sheriff’s deputy who at­
`tempted to apprehend them. Hall received the death
`penalty for both murders, although his sentence for the
`Coburn murder was later reduced on account of insuffi­
`cient evidence of premeditation. Hall v. Florida, 403
`
`
`
`

`
`2
`
`
`HALL v. FLORIDA
`
`Opinion of the Court
`So. 2d 1319, 1321 (Fla. 1981) (per curiam).
`
`
`
`Hall argues that he cannot be executed because of his
`intellectual disability. Previous opinions of this Court
`have employed the term “mental retardation.” This opin­
`ion uses the term “intellectual disability” to describe the
`identical phenomenon. See Rosa’s Law, 124 Stat. 2643
`(changing entries in the U. S. Code from “mental retarda­
`tion” to “intellectual disability”); Schalock et. al, The Re­
`naming of Mental Retardation: Understanding the Change
`
`to the Term Intellectual Disability, 45 Intellectual & De­
`velopmental Disabilities 116 (2007). This change in ter­
`minology is approved and used in the latest edition of the
`
`Diagnostic and Statistical Manual of Mental Disorders,
`
`one of the basic texts used by psychiatrists and other
`experts; the manual is often referred to by its initials
`“DSM,” followed by its edition number, e.g., “DSM–5.” See
`American Psychiatric Association, Diagnostic and Statisti­
`cal Manual of Mental Disorders 33 (5th ed. 2013).
`
`When Hall was first sentenced, this Court had not yet
`ruled that the Eighth Amendment prohibits States from
`imposing the death penalty on persons with intellectual
`disability. See Penry v. Lynaugh, 492 U. S. 302, 340
`(1989). And at the time, Florida law did not consider
`intellectual disability as a statutory mitigating factor.
`
`After this Court held that capital defendants must be
`permitted to present nonstatutory mitigating evidence in
`death penalty proceedings, Hitchcock v. Dugger, 481 U. S.
`393, 398–399 (1987), Hall was resentenced. Hall then
`presented substantial and unchallenged evidence of intel­
`lectual disability. School records indicated that his teach­
`ers identified him on numerous occasions as “[m]entally
`
`retarded.” App. 482–483. Hall had been prosecuted for a
`different, earlier crime. His lawyer in that matter later
`testified that the lawyer “[c]ouldn’t really understand
`
`
`anything [Hall] said.” Id., at 480. And, with respect to the
`murder trial given him in this case, Hall’s counsel recalled
`
`
`
`
`
`

`
`3
`
`
`
`
`
`
`
`
`
`
`
` Cite as: 572 U. S. ____ (2014)
`
`Opinion of the Court
`that Hall could not assist in his own defense because he
`had “‘a mental . . . level much lower than his age,’” at best
`comparable to the lawyer’s 4-year-old daughter. Brief for
`Petitioner 11. A number of medical clinicians testified
`that, in their professional opinion, Hall was “significantly
`retarded,” App. 507; was “mentally retarded,” id., at 517;
`and had levels of understanding “typically [seen] with
`toddlers,” id., at 523.
`
`As explained below in more detail, an individual’s abil­
`ity or lack of ability to adapt or adjust to the requirements
`of daily life, and success or lack of success in doing so, is
`central to the framework followed by psychiatrists and
`other professionals in diagnosing intellectual disability.
`See DSM–5, at 37. Hall’s siblings testified that there was
`something “very wrong” with him as a child. App. 466.
`Hall was “slow with speech and . . . slow to learn.” Id., at
`490. He “walked and talked long after his other brothers
`and sisters,” id., at 461, and had “great difficulty forming
`his words,” id., at 467.
`
`Hall’s upbringing appeared to make his deficits in adap­
`tive functioning all the more severe. Hall was raised—in
`the words of the sentencing judge—“under the most horri­
`ble family circumstances imaginable.” Id., at 53. Al­
`though “[t]eachers and siblings alike immediately recog­
`nized [Hall] to be significantly mentally retarded . . . [t]his
`retardation did not garner any sympathy from his mother,
`
`
`but rather caused much scorn to befall him.” Id., at 20.
`Hall was “[c]onstantly beaten because he was ‘slow’ or
`because he made simple mistakes.” Ibid. His mother
`“would strap [Hall] to his bed at night, with a rope thrown
`over a rafter. In the morning, she would awaken Hall by
`hoisting him up and whipping him with a belt, rope, or
`cord.” Ibid. Hall was beaten “ten or fifteen times a week
`sometimes.” Id., at 477. His mother tied him “in a ‘croaker’
`sack, swung it over a fire, and beat him,” “buried him
`
`in the sand up to his neck to ‘strengthen his legs,’” and
`
`
`
`
`
`
`
`
`
`

`
`4
`
`
`HALL v. FLORIDA
`
`Opinion of the Court
`“held a gun on Hall . . . while she poked [him] with sticks.”
`Hall v. Florida, 614 So. 2d 473, 480 (Fla. 1993) (Barkett,
`C. J., dissenting).
`The jury, notwithstanding this testimony, voted to
`
`
`sentence Hall to death, and the sentencing court adopted
`the jury’s recommendation. The court found that there
`was “substantial evidence in the record” to support the
`finding that “Freddie Lee Hall has been mentally retarded
`his entire life.” App. 46. Yet the court also “suspect[ed]
`
`
`that the defense experts [were] guilty of some professional
`overkill,” because “[n]othing of which the experts testified
`could explain how a psychotic, mentally-retarded, brain­
`damaged, learning-disabled, speech-impaired person could
`formulate a plan whereby a car was stolen and a conven­
`ience store was robbed.” Id., at 42. The sentencing court
`went on to state that, even assuming the expert testimony
`
`to be accurate, “the learning disabilities, mental retarda­
`tion, and other mental difficulties . . . cannot be used to
`justify, excuse or extenuate the moral culpability of the
`defendant in this cause.” Id., at 56. Hall was again sen­
`tenced to death. The Florida Supreme Court affirmed,
`concluding that “Hall’s argument that his mental retarda­
`tion provided a pretense of moral or legal justification”
`had “no merit.” Hall, 614 So. 2d, at 478. Chief Justice
`Barkett dissented, arguing that executing a person with
`intellectual disability violated the State Constitution’s
`prohibition on cruel and unusual punishment. Id., at 481–
`482.
`
`In 2002, this Court ruled that the Eighth Amendment
`prohibited the execution of persons with intellectual disa­
`bility. Atkins v. Virginia, 536 U. S., at 321. On November
`30, 2004, Hall filed a motion claiming that he had intellec­
`tual disability and could not be executed. More than five
`years later, Florida held a hearing to consider Hall’s mo­
`tion. Hall again presented evidence of intellectual disabil­
`ity, including an IQ test score of 71. (Hall had received
`
`
`
`
`
`
`
`

`
`
`
` Cite as: 572 U. S. ____ (2014)
`
`Opinion of the Court
`nine IQ evaluations in 40 years, with scores ranging from
`60 to 80, Brief for Respondent 8, but the sentencing court
`excluded the two scores below 70 for evidentiary reasons,
`leaving only scores between 71 and 80. See App. 107; 109
`So. 3d 704, 707 (Fla. 2012)). In response, Florida argued
`that Hall could not be found intellectually disabled be­
`cause Florida law requires that, as a threshold matter,
`Hall show an IQ test score of 70 or below before presenting
`any additional evidence of his intellectual disability. App.
`278–279 (“[U]nder the law, if an I. Q. is above 70, a person
`is not mentally retarded”). The Florida Supreme Court
`rejected Hall’s appeal and held that Florida’s 70-point
`threshold was constitutional. 109 So. 3d, at 707–708.
`This Court granted certiorari. 571 U. S. ___ (2013).
`
`II
`
`The Eighth Amendment provides that “[e]xcessive bail
`
`shall not be required, nor excessive fines imposed, nor
`cruel and unusual punishments inflicted.” The Four­
`teenth Amendment applies those restrictions to the
`
`States. Roper v. Simmons, 543 U. S. 551, 560 (2005);
`Furman v. Georgia, 408 U. S. 238, 239–240 (1972) (per
`
`curiam). “By protecting even those convicted of heinous
`crimes, the Eighth Amendment reaffirms the duty of the
`
`
` government to respect the dignity of all persons.” Roper,
`supra, at 560; see also Trop v. Dulles, 356 U. S. 86, 100
`(1958) (plurality opinion) (“The basic concept underlying
`the Eighth Amendment is nothing less than the dignity of
`man”).
`
`The Eighth Amendment “is not fastened to the obsolete
`
`but may acquire meaning as public opinion becomes en­
`lightened by a humane justice.” Weems v. United States,
`217 U. S. 349, 378 (1910). To enforce the Constitution’s
`protection of human dignity, this Court looks to the “evolv­
`ing standards of decency that mark the progress of a
`maturing society.” Trop, supra, at 101. The Eighth
`
`
`
`
`
`
`
`5
`
`

`
`HALL v. FLORIDA
`
`Opinion of the Court
`Amendment’s protection of dignity reflects the Nation we
`
`have been, the Nation we are, and the Nation we aspire to
`be. This is to affirm that the Nation’s constant, unyielding
`purpose must be to transmit the Constitution so that its
`precepts and guarantees retain their meaning and force.
`
`The Eighth Amendment prohibits certain punishments
`as a categorical matter. No natural-born citizen may be
`denaturalized. Ibid. No person may be sentenced to death
`
`for a crime committed as a juvenile. Roper, supra, at 578.
`And, as relevant for this case, persons with intellectual
`disability may not be executed. Atkins, 536 U. S., at 321.
`
`
`
`No legitimate penological purpose is served by executing
`a person with intellectual disability. Id., at 317, 320. 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. “[P]unishment is justified under one or more of
`three principal rationales: rehabilitation, deterrence, and
`retribution.” Kennedy v. Louisiana, 554 U. S. 407, 420
`(2008). Rehabilitation, it is evident, is not an applicable
`
`rationale for the death penalty. See Gregg v. Georgia, 428
`U. S. 153, 183 (1976) (joint opinion of Stewart, Powell, and
`
`Stevens, JJ.). As for deterrence, those with intellectual
`disability are, by reason of their condition, likely unable to
`make the calculated judgments that are the premise for
`the deterrence rationale. They have a “diminished ability”
`to “process information, to learn from experience, to en­
`gage in logical reasoning, or to control impulses . . .
`
`[which] make[s] it less likely that they can process the
`information of the possibility of execution as a penalty
`and, as a result, control their conduct based upon that
`information.” Atkins, 536 U. S., at 320. Retributive val­
`ues are also ill-served by executing those with intellectual
`
`disability. The diminished capacity of the intellectually
`disabled lessens moral culpability and hence the retribu­
`tive value of the punishment. See id., at 319 (“If the cul­
`
`
`
`6
`
`
`
`
`
`
`

`
`
`
` Cite as: 572 U. S. ____ (2014)
`
`Opinion of the Court
`pability of the average murderer is insufficient to justify
`the most extreme sanction available to the State, the
`lesser culpability of the mentally retarded offender surely
`does not merit that form of retribution”).
`
`
`A further reason for not imposing the death penalty on a
`person who is intellectually disabled is to protect the
`integrity of the trial process. These persons face “a special
`risk of wrongful execution” because they are more likely to
`give false confessions, are often poor witnesses, and are
`
`less able to give meaningful assistance to their counsel.
`Id., at 320–321. This is not to say that under current law
`persons with intellectual disability who “meet the law’s
`requirements for criminal responsibility” may not be tried
`and punished. Id., at 306. They may not, however, re­
`ceive the law’s most severe sentence. Id., at 318.
`
`The question this case presents is how intellectual
`disability must be defined in order to implement these
`principles and the holding of Atkins. To determine if
`Florida’s cutoff rule is valid, it is proper to consider the
`psychiatric and professional studies that elaborate on the
`purpose and meaning of IQ scores to determine how the
`scores relate to the holding of Atkins. This in turn leads to
`a better understanding of how the legislative policies of
`various States, and the holdings of state courts, imple­
`ment the Atkins rule. That understanding informs our
`
`determination whether there is a consensus that instructs
`how to decide the specific issue presented here. And, in
`conclusion, this Court must express its own independent
`determination reached in light of the instruction found in
`those sources and authorities.
`
`
`III
`
`A
`
`That this Court, state courts, and state legislatures
`
`consult and are informed by the work of medical experts in
`determining intellectual disability is unsurprising. Those
`
`
`
`
`
`
`
`7
`
`

`
`8
`
`
`HALL v. FLORIDA
`
`Opinion of the Court
`professionals use their learning and skills to study and
`consider the consequences of the classification schemes
`they devise in the diagnosis of persons with mental or
`psychiatric disorders or disabilities. Society relies upon
`medical and professional expertise to define and explain
`how to diagnose the mental condition at issue. And the
`definition of intellectual disability by skilled professionals
`has implications far beyond the confines of the death
`penalty: for it is relevant to education, access to social
`programs, and medical treatment plans. In determining
`
`who qualifies as intellectually disabled, it is proper to
`consult the medical community’s opinions.
`
`As the Court noted in Atkins, the medical community
`defines intellectual disability according to three criteria:
`significantly subaverage intellectual functioning, deficits
`in adaptive functioning (the inability to learn basic skills
`and adjust behavior to changing circumstances), and onset
`of these deficits during the developmental period. See id.,
`at 308, n. 3; DSM–5, at 33; Brief for American Psychologi­
`
`cal Association et al. as Amici Curiae 12–13 (hereinafter
`
`APA Brief). This last factor, referred to as “age of onset,”
`is not at issue.
`
`The first and second criteria—deficits in intellectual
`functioning and deficits in adaptive functioning—are
`central here. In the context of a formal assessment, “[t]he
`existence of concurrent deficits in intellectual and adap­
`tive functioning has long been the defining characteristic
`of intellectual disability.” Id., at 11.
`
`On its face, the Florida statute could be consistent with
`the views of the medical community noted and discussed
`in Atkins. Florida’s statute defines intellectual disability
`for purposes of an Atkins proceeding as “significantly
`subaverage general intellectual functioning existing con­
`
`currently with deficits in adaptive behavior and manifested
`during the period from conception to age 18.” Fla. Stat.
`§921.137(1) (2013). The statute further defines “signifi­
`
`
`
`
`
`
`
`
`
`

`
`
`
` Cite as: 572 U. S. ____ (2014)
`
`Opinion of the Court
` cantly subaverage general intellectual functioning” as
`
`“performance that is two or more standard deviations from
`the mean score on a standardized intelligence test.” Ibid.
`The mean IQ test score is 100. The concept of standard
`deviation describes how scores are dispersed in a popula­
`tion. Standard deviation is distinct from standard error of
`
`measurement, a concept which describes the reliability of
`a test and is discussed further below. The standard devia­
`tion on an IQ test is approximately 15 points, and so two
`standard deviations is approximately 30 points. Thus a
`
`test taker who performs “two or more standard deviations
`from the mean” will score approximately 30 points below
`the mean on an IQ test, i.e., a score of approximately 70
`points.
`On its face this statute could be interpreted consistently
`
`with Atkins and with the conclusions this Court reaches in
`the instant case. Nothing in the statute precludes Florida
`from taking into account the IQ test’s standard error of
`measurement, and as discussed below there is evidence
`that Florida’s Legislature intended to include the meas­
`urement error in the calculation. But the Florida Su­
`preme Court has interpreted the provisions more nar­
`rowly. It has held that a person whose test score is above 70,
`including a score within the margin for measurement
`error, does not have an intellectual disability and is barred
`from presenting other evidence that would show his facul­
`
` ties are limited. See Cherry v. State, 959 So. 2d 702, 712–
`713 (Fla. 2007) (per curiam). That strict IQ test score
`cutoff of 70 is the issue in this case.
`
`
`Pursuant to this mandatory cutoff, sentencing courts
`cannot consider even substantial and weighty evidence of
`intellectual disability as measured and made manifest by
`the defendant’s failure or inability to adapt to his social
`and cultural environment, including medical histories,
`behavioral records, school tests and reports, and testimony
`regarding past behavior and family circumstances. This is
`
`
`
`
`
`
`
`9
`
`

`
`HALL v. FLORIDA
`
`Opinion of the Court
`so even though the medical community accepts that all of
`this evidence can be probative of intellectual disability,
`including for individuals who have an IQ test score above
`70. See APA Brief 15–16 (“[T]he relevant clinical authori­
`ties all agree that an individual with an IQ score above 70
`may properly be diagnosed with intellectual disability if
`significant limitations in adaptive functioning also exist”);
`
`DSM–5, at 37 (“[A] person with an IQ score above 70 may
`
`have such severe adaptive behavior problems . . . that the
`person’s actual functioning is comparable to that of indi­
`viduals with a lower IQ score”).
`
`Florida’s rule disregards established medical practice in
`
`two interrelated ways. It takes an IQ score as final and
`conclusive evidence of a defendant’s intellectual capacity,
`when experts in the field would consider other evidence.
`It also relies on a purportedly scientific measurement of
`the defendant’s abilities, his IQ score, while refusing to
`recognize that the score is, on its own terms, imprecise.
`The professionals who design, administer, and interpret
`
`IQ tests have agreed, for years now, that IQ test scores
`should be read not as a single fixed number but as a
`range. See D. Wechsler, The Measurement of Adult Intel­
`ligence 133 (3d ed. 1944) (reporting the range of error on
`an early IQ test). Each IQ test has a “standard error of
`measurement,” ibid., often referred to by the abbreviation
`“SEM.” A test’s SEM is a statistical fact, a reflection of
`the inherent imprecision of the test itself. See R. Furr &
`V. Bacharach, Psychometrics 118 (2d ed. 2014) (identify­
`ing the SEM as “one of the most important concepts in
`measurement theory”). An individual’s IQ test score on
`any given exam may fluctuate for a variety of reasons.
`
`These include the test-taker’s health; practice from earlier
`tests; the environment or location of the test; the examin­
`er’s demeanor; the subjective judgment involved in scoring
`certain questions on the exam; and simple lucky guessing.
`
`See American Association on Intellectual and Develop­
`
`
`
`
`
`
`
`
`
`
`
`
`
`10
`
`
`

`
`
`
` Cite as: 572 U. S. ____ (2014)
`
`Opinion of the Court
`mental Disabilities, R. Schalock et al., User’s Guide To
`Accompany the 11th Edition of Intellectual Disability:
`Definition, Classification, and Systems of Supports 22
`(2012) (hereinafter AAIDD Manual); A. Kaufman, IQ
`Testing 101, pp. 138–139 (2009).
`
`The SEM reflects the reality that an individual’s intel­
`lectual functioning cannot be reduced to a single numeri­
`cal score. For purposes of most IQ tests, the SEM means
`
`that an individual’s score is best understood as a range of
`scores on either side of the recorded score. The SEM
`allows clinicians to calculate a range within which one
`may say an individual’s true IQ score lies. See APA Brief
`23 (“SEM is a unit of measurement: 1 SEM equates to a
`confidence of 68% that the measured score falls within a
`given score range, while 2 SEM provides a 95% confidence
`level that the measured score is within a broader range”).
`A score of 71, for instance, is generally considered to re­
`
`flect a range between 66 and 76 with 95% confidence and a
`range of 68.5 and 73.5 with a 68% confidence. See DSM–
`5, at 37 (“Individuals with intellectual disability have
`scores of approximately two standard deviations or more
`below the population mean, including a margin for meas­
`urement error (generally +5 points). . . . [T]his involves a
`
`score of 65–75 (70 ± 5)”); APA Brief 23 (“For example, the
`average SEM for the WAIS-IV is 2.16 IQ test points and
`the average SEM for the Stanford-Binet 5 is 2.30 IQ test
`points (test manuals report SEMs by different age group­
`ings; these scores are similar, but not identical, often due
`to sampling error)”). Even when a person has taken mul­
`tiple tests, each separate score must be assessed using the
`
`
`SEM, and the analysis of multiple IQ scores jointly is a
`complicated endeavor. See Schneider, Principles of As­
`sessment of Aptitude and Achievement, in The Oxford
`
`Handbook of Child Psychological Assessment 286, 289–
`
`291, 318 (D. Saklofske, C. Reynolds, V. Schwean, eds.
`
`2013). In addition, because the test itself may be flawed,
`
`
`
`
`
`
`
`
`
`
`
` 11
`
`
`
`
`
`

`
`12
`
`
`HALL v. FLORIDA
`
`Opinion of the Court
`or administered in a consistently flawed manner, multiple
`examinations may result in repeated similar scores, so
`
`that even a consistent score is not conclusive evidence of
`intellectual functioning.
`
`Despite these professional explanations, Florida law
`used the test score as a fixed number, thus barring further
`consideration of other evidence bearing on the question of
`intellectual disability. For professionals to diagnose—and
`for the law then to determine—whether an intellectual
`disability exists once the SEM applies and the individual’s
`
`IQ score is 75 or below the inquiry would consider factors
`indicating whether the person had deficits in adaptive
`functioning. These include evidence of past performance,
`
`environment, and upbringing.
`B
`
`A significant majority of States implement the protec­
`tions of Atkins by taking the SEM into account, thus
`acknowledging the error inherent in using a test score
`without necessary adjustment. This calculation provides
`“objective indicia of society’s standards” in the context of
`the Eighth Amendment. Roper, 543 U. S., at 563. Only
`the Kentucky and Virginia Legislatures have adopted a
`
`fixed score cutoff identical to Florida’s. Ky. Rev. Stat.
`Ann. §532.130(2) (Lexis Supp. 2013); Bowling v. Com-
`monwealth, 163 S. W. 3d 361, 375 (Ky. 2005); Va. Code
`Ann. §19.2–264.3:1.1 (Lexis Supp. 2013); Johnson v.
`Commonwealth, 267 Va. 53, 75, 591 S. E. 2d 47, 59 (2004),
`vacated and remanded on other grounds, 544 U. S. 901
`(2005). Alabama also may use a strict IQ score cutoff at
`
`70, although not as a result of legislative action. See
`Smith v. State, 71 So. 3d 12, 20 (Ala. Crim. App. 2008)
`(“The Alabama Supreme Court . . . did not adopt any
`‘margin of error’ when examining a defendant’s IQ score”).
`Petitioner does not question the rule in States which use a
`bright-line cutoff at 75 or greater, Tr. of Oral Arg. 9, and
`
`
`
`
`
`
`
`

`
`
`
`
`
` 13
`
`
`
` Cite as: 572 U. S. ____ (2014)
`
`Opinion of the Court
`so they are not included alongside Florida in this analysis.
`
`In addition to these States, Arizona, Delaware, Kansas,
`North Carolina, and Washington have statutes which
`could be interpreted to provide a bright-line cutoff leading
`to the same result that Florida mandates in its cases. See
`Ariz. Rev. Stat. Ann. §13–753(F) (West 2013); Del. Code
`Ann. Tit. 11, §4209(d)(3) (2012 Supp.); Kan. Stat. Ann.
`§76–12b01 (2013 Supp.); N. C. Gen. Stat. Ann. §15A–2005
`
`(Lexis 2013); Wash. Rev. Code §10.95.030(2)(c) (2012).
`That these state laws might be interpreted to require a
`bright-line cutoff does not mean that they will be so inter­
`pret