Hall v. Florida ( 2014 )


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  • (Slip Opinion)              OCTOBER TERM, 2013                                       1
    Syllabus
    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
    2                            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
    Cite as: 572 U. S. ____ (2014)                      3
    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.
    Cite as: 572 U. S. ____ (2014)                              1
    Opinion of the Court
    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
    Cite as: 572 U. S. ____ (2014)             3
    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)            5
    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
    6                     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
    Cite as: 572 U. S. ____ (2014)            7
    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
    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)            9
    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
    10                    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
    Cite as: 572 U. S. ____ (2014)          11
    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,
    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
    Cite as: 572 U. S. ____ (2014)           13
    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
    preted, however. See, e.g., State v. Vela, 
    279 Neb. 94
    , 126,
    137, 
    777 N.W.2d 266
    , 292, 299 (2010) (Although Nebras­
    ka’s statute specifies “[a]n intelligence quotient of seventy
    or below on a reliably administered intelligence quotient
    test,” “[t]he district court found that [the defendant’s]
    score of 75 on the [IQ test], considered in light of the
    standard error of measurement, could be considered as
    subaverage general intellectual functioning for purposes of
    diagnosing mental retardation”).
    Arizona’s statute appears to set a broad statutory cutoff
    at 70, Ariz. Rev. Stat. Ann. §13–753(F) (West 2013), but
    another provision instructs courts to “take into account
    the margin of error for a test administered.” 
    Id. at §14­
    753(K)(5). How courts are meant to interpret the statute
    in a situation like Hall’s is not altogether clear. The prin­
    cipal Arizona case on the matter, State v. Roque, 
    141 P.3d 368
    , (Ariz 2006), states that “the statute accounts for
    margin of error by requiring multiple tests,” and that “if
    the defendant achieves a full-scale score of 70 or below on
    any one of the tests, then the court proceeds to a hearing.”
    
    Id. at 403.
    But that case also notes that the defendant
    had an IQ score of 80, well outside the margin of error,
    and that all but one of the sub-parts of the IQ test were
    “above 75.” 
    Id. Kansas has
    not had an execution in almost five decades,
    14                   HALL v. FLORIDA
    Opinion of the Court
    and so its laws and jurisprudence on this issue are unlikely
    to receive attention on this specific question. See 
    Atkins, 536 U.S., at 316
    (“[E]ven in those States that allow the
    execution of mentally retarded offenders, the practice
    is uncommon. Some States . . . continue to authorize
    executions, but none have been carried out in decades.
    Thus there is little need to pursue legislation barring the
    execution of the mentally retarded in those States”).
    Delaware has executed three individuals in the past dec­
    ade, while Washington has executed one person, and has
    recently suspended its death penalty. None of the four
    individuals executed recently in those States appears to
    have brought a claim similar to that advanced here.
    Thus, at most nine States mandate a strict IQ score
    cutoff at 70. Of these, four States (Delaware, Kansas,
    North Carolina, and Washington) appear not to have
    considered the issue in their courts. On the other side of
    the ledger stand the 18 States that have abolished the
    death penalty, either in full or for new offenses, and Ore­
    gon, which has suspended the death penalty and executed
    only two individuals in the past 40 years. See 
    Roper, 543 U.S., at 574
    (“[The] Court should have considered those
    States that had abandoned the death penalty altogether as
    part of the consensus against the juvenile death penalty”).
    In those States, of course, a person in Hall’s position
    could not be executed even without a finding of intellectual
    disability. Thus in 41 States an individual in Hall’s
    position—an individual with an IQ score of 71—would not
    be deemed automatically eligible for the death penalty.
    These aggregate numbers are not the only considera­
    tions bearing on a determination of consensus. Consistency
    of the direction of change is also relevant. See 
    id., at 565–566
    (quoting 
    Atkins, supra, at 315
    ). Since Atkins,
    many States have passed legislation to comply with the
    constitutional requirement that persons with intellectual
    disability not be executed. Two of these States, Virginia
    Cite as: 572 U. S. ____ (2014)          15
    Opinion of the Court
    and Delaware, appear to set a strict cutoff at 70, although
    as discussed, Delaware’s courts have yet to interpret the
    law. In contrast, at least 11 States have either abolished
    the death penalty or passed legislation allowing defend­
    ants to present additional evidence of intellectual disabil­
    ity when their IQ test score is above 70.
    Since Atkins, five States have abolished the death pen­
    alty through legislation. See 2012 Conn. Pub. Acts no. 12–
    5; Ill. Comp. Stat. ch. 725, §119–1 (West 2012); Md. Cor­
    rec. Servs. Code Ann. §3–901 et seq. (Lexis 2008); N. J.
    Stat. Ann. §2C:11–3(b)(1) (West Supp. 2013); 2009 N. M.
    Laws ch. 11, §§5–7. In addition, the New York Court of
    Appeals invalidated New York’s death penalty under the
    State Constitution in 2004, see People v. LeValle, 
    3 N.Y. 3d
    88, 
    817 N.E.2d 341
    (2004), and legislation has not
    been passed to reinstate it. And when it did impose the
    death penalty, New York did not employ an IQ cutoff in
    determining intellectual disability. N. Y. Crim. Proc. Law
    Ann. §400.27(12)(e) (West 2005).
    In addition to these States, at least five others have
    passed legislation allowing a defendant to present addi­
    tional evidence of intellectual disability even when an IQ
    test score is above 70. See Cal. Penal Code Ann. §1376
    (West Supp. 2014) (no IQ cutoff); Idaho Code §19–2515A
    (Lexis Supp. 2013) (“seventy (70) or below”); Pizzutto v.
    State, 
    146 Idaho 720
    , 729, 
    202 P.3d 642
    , 651 (2008) (“The
    alleged error in IQ testing is plus or minus five points.
    The district court was entitled to draw reasonable infer­
    ences from the undisputed facts”); La. Code Crim. Proc.
    Ann., Art. 905.5.1 (West Supp. 2014) (no IQ cutoff); Nev.
    Rev. Stat. §174.098.7 (2013) (no IQ cutoff); Utah Code Ann
    §77–15a–102 (Lexis 2012) (no IQ cutoff). The U. S. Code
    likewise does not set a strict IQ cutoff. See 
    18 U.S. C
    .
    §3596(c). And no State that previously allowed defendants
    with an IQ score over 70 to present additional evidence of
    intellectual disability has modified its law to create a
    16                    HALL v. FLORIDA
    Opinion of the Court
    strict cutoff at 70. Cf. 
    Roper, supra, at 566
    (“Since Stan-
    ford v. Kentucky, 
    492 U.S. 361
    (1989), no State that previ­
    ously prohibited capital punishment for juveniles has
    reinstated it”).
    In summary, every state legislature to have considered
    the issue after Atkins—save Virginia’s—and whose law
    has been interpreted by its courts has taken a position
    contrary to that of Florida. Indeed, the Florida Legisla­
    ture, which passed the relevant legislation prior to Atkins,
    might well have believed that its law would not create
    a fixed cutoff at 70. The staff analysis accompanying
    the 2001 bill states that it “does not contain a set IQ
    level . . . . Two standard deviations from these tests is ap­
    proximately a 70 IQ, although it can be extended up to
    75.” Fla. Senate Staff Analysis and Economic Impact
    Statement, CS/SB 238, p. 11 (Feb. 14, 2001). But the
    Florida Supreme Court interpreted the law to require a
    bright-line cutoff at 70, see 
    Cherry, 959 So. 2d, at 712
    –713,
    and the Court is bound by that interpretation.
    The rejection of the strict 70 cutoff in the vast majority
    of States and the “consistency in the trend,” 
    Roper, supra, at 567
    , toward recognizing the SEM provide strong evi­
    dence of consensus that our society does not regard this
    strict cutoff as proper or humane.
    C
    Atkins itself acknowledges the inherent error in IQ
    testing. It is true that Atkins “did not provide definitive
    procedural or substantive guides for determining when a
    person who claims mental retardation” falls within the
    protection of the Eighth Amendment. Bobby v. Bies, 
    556 U.S. 825
    , 831 (2009). 	In Atkins, the Court stated:
    “Not all people who claim to be mentally retarded will
    be so impaired as to fall within the range of mentally
    retarded offenders about whom there is a national
    consensus. As was our approach in Ford v. Wain-
    Cite as: 572 U. S. ____ (2014)           17
    Opinion of the Court
    wright with regard to insanity, ‘we leave to the
    State[s] the task of developing appropriate ways to en­
    force the constitutional restriction upon [their] execu­
    tion of sentences.’ 
    536 U.S., at 317
    (quoting Ford v.
    Wainwright, 
    477 U.S. 399
    , 416–417 (1986); citation
    omitted).
    As discussed above, the States play a critical role in ad­
    vancing protections and providing the Court with infor­
    mation that contributes to an understanding of how intel­
    lectual disability should be measured and assessed. But
    Atkins did not give the States unfettered discretion to
    define the full scope of the constitutional protection.
    The Atkins Court twice cited definitions of intellectual
    disability which, by their express terms, rejected a strict
    IQ test score cutoff at 70. Atkins first cited the definition
    provided in the DSM–IV: “ ‘Mild’ mental retardation is
    typically used to describe people with an IQ level of 50–55
    to approximately 
    70.” 536 U.S., at 308
    , n. 3 (citing Diag­
    nostic and Statistical Manual of Mental Disorders 41 (4th
    ed. 2000)). The Court later noted that “ ‘an IQ between 70
    and 75 or lower . . . is typically considered the cutoff IQ
    score for the intellectual function prong of the mental
    retardation definition.’ 
    536 U.S., at 309
    , n. 5. Further­
    more, immediately after the Court declared that it left “ ‘to
    the States the task of developing appropriate ways to
    enforce the constitutional restriction,’ ” 
    id., at 317,
    the
    Court stated in an accompanying footnote that “[t]he
    [state] statutory definitions of mental retardation are not
    identical, but generally conform to the clinical definitions,”
    
    ibid. Thus Atkins itself
    not only cited clinical definitions for
    intellectual disability but also noted that the States’
    standards, on which the Court based its own conclusion,
    conformed to those definitions. In the words of Atkins,
    those persons who meet the “clinical definitions” of intel­
    18                    HALL v. FLORIDA
    Opinion of the Court
    lectual disability “by definition . . . have diminished capac­
    ities to understand and process information, to communi­
    cate, to abstract from mistakes and learn from experience,
    to engage in logical reasoning, to control impulses, and to
    understand the reactions of others.” 
    Id., at 318.
    Thus,
    they bear “diminish[ed] . . . personal culpability.” 
    Ibid. The clinical definitions
    of intellectual disability, which
    take into account that IQ scores represent a range, not a
    fixed number, were a fundamental premise of Atkins. And
    those clinical definitions have long included the SEM. See
    Diagnostic and Statistical Manual of Mental Disorders 28
    (rev. 3d ed. 1987) (“Since any measurement is fallible, an
    IQ score is generally thought to involve an error of meas­
    urement of approximately five points; hence, an IQ of 70 is
    considered to represent a band or zone of 65 to 75. Treat­
    ing the IQ with some flexibility permits inclusion in the
    Mental Retardation category of people with IQs somewhat
    higher than 70 who exhibit significant deficits in adaptive
    behavior”).
    Respondent argues that the current Florida law was
    favorably cited by the Atkins Court. See Brief for Re­
    spondent 18 (“As evidence of the national consensus, the
    Court specifically cited Florida’s statute at issue here,
    which has not substantively changed”). While Atkins did
    refer to Florida’s law in a citation listing States which had
    outlawed the execution of the intellectually 
    disabled, 536 U.S., at 315
    , that fleeting mention did not signal the
    Court’s approval of Florida’s current understanding of the
    law. As discussed above, when Atkins was decided the
    Florida Supreme Court had not yet interpreted the law to
    require a strict IQ cutoff at 70. That new interpretation
    runs counter to the clinical definition cited throughout
    Atkins and to Florida’s own legislative report indicating
    this kind of cutoff need not be used.
    Respondent’s argument also conflicts with the logic of
    Atkins and the Eighth Amendment. If the States were to
    Cite as: 572 U. S. ____ (2014)          19
    Opinion of the Court
    have complete autonomy to define intellectual disability as
    they wished, the Court’s decision in Atkins could become a
    nullity, and the Eighth Amendment’s protection of human
    dignity would not become a reality. This Court thus reads
    Atkins to provide substantial guidance on the definition of
    intellectual disability.
    D
    The actions of the States and the precedents of this
    Court “give us essential instruction,” 
    Roper, 543 U.S., at 564
    , but the inquiry must go further. “[T]he Constitution
    contemplates that in the end our own judgment will be
    brought to bear on the question of the acceptability of the
    death penalty under the Eighth Amendment.” Coker v.
    Georgia, 
    433 U.S. 584
    , 597 (1977) (plurality opinion).
    That exercise of independent judgment is the Court’s
    judicial duty. See 
    Roper, supra, at 574
    (“[T]o the extent
    Stanford was based on a rejection of the idea that this
    Court is required to bring its independent judgment to
    bear on the proportionality of the death penalty for a
    particular class of crimes or offenders, it suffices to note
    that this rejection was inconsistent with prior Eighth
    Amendment decisions” (citation omitted).
    In this Court’s independent judgment, the Florida stat­
    ute, as interpreted by its courts, is unconstitutional.
    In addition to the views of the States and the Court’s
    precedent, this determination is informed by the views of
    medical experts. These views do not dictate the Court’s
    decision, yet the Court does not disregard these informed
    assessments. See Kansas v. Crane, 
    534 U.S. 407
    , 413
    (2002) (“[T]he science of psychiatry . . . informs but does
    not control ultimate legal determinations . . .”). It is the
    Court’s duty to interpret the Constitution, but it need not
    do so in isolation. The legal determination of intellectual
    disability is distinct from a medical diagnosis, but it is
    informed by the medical community’s diagnostic frame­
    20                    HALL v. FLORIDA
    Opinion of the Court
    work. Atkins itself points to the diagnostic criteria em­
    ployed by psychiatric professionals. And the professional
    community’s teachings are of particular help in this case,
    where no alternative definition of intellectual disability is
    presented and where this Court and the States have
    placed substantial reliance on the expertise of the medical
    profession.
    By failing to take into account the SEM and setting a
    strict cutoff at 70, Florida “goes against the unanimous
    professional consensus.” APA Brief 15. Neither Florida
    nor its amici point to a single medical professional who
    supports this cutoff. The DSM–5 repudiates it: “IQ test
    scores are approximations of conceptual functioning but
    may be insufficient to assess reasoning in real-life situa­
    tions and mastery of practical tasks.” DSM–5, at 37. This
    statement well captures the Court’s independent assess­
    ment that an individual with an IQ test score “between 70
    and 75 or lower,” 
    Atkins, supra, at 309
    , n. 5, may show
    intellectual disability by presenting additional evidence
    regarding difficulties in adaptive functioning.
    The flaws in Florida’s law are the result of the inherent
    error in IQ tests themselves. An IQ score is an approxi­
    mation, not a final and infallible assessment of intellectual
    functioning. See APA Brief 24 (“[I]t is standard pyscho­
    metric practice to report the ‘estimates of relevant reliabil­
    ities and standard errors of measurement’ when reporting
    a test score”); 
    ibid. (the margin of
    error is “inherent to the
    accuracy of IQ scores”); Furr, Psychometrics, at 119
    (“[T]he standard error of measurement is an important
    psychometric value with implications for applied meas­
    urement”). SEM is not a concept peculiar to the psychiat­
    ric profession and IQ tests. It is a measure that is recog­
    nized and relied upon by those who create and devise tests
    of all sorts. 
    Id., at 118
    (identifying the SEM as “one of the
    most important concepts in measurement theory”).
    This awareness of the IQ test’s limits is of particular
    Cite as: 572 U. S. ____ (2014)           21
    Opinion of the Court
    importance when conducting the conjunctive assessment
    necessary to assess an individual’s intellectual ability.
    See American Association on Intellectual and Develop­
    mental Disabilities, Intellectual Disability: Definition,
    Classification, and Systems of Supports 40 (11th ed. 2010)
    (“It must be stressed that the diagnosis of [intellectual
    disability] is intended to reflect a clinical judgment rather
    than an actuarial determination”).
    Intellectual disability is a condition, not a number. See
    DSM–5, at 37. Courts must recognize, as does the medical
    community, that the IQ test is imprecise. This is not to
    say that an IQ test score is unhelpful. It is of considerable
    significance, as the medical community recognizes. But in
    using these scores to assess a defendant’s eligibility for the
    death penalty, a State must afford these test scores the
    same studied skepticism that those who design and use
    the tests do, and understand that an IQ test score repre­
    sents a range rather than a fixed number. A State that
    ignores the inherent imprecision of these tests risks exe­
    cuting a person who suffers from intellectual disability.
    See APA Brief 17 (“Under the universally accepted clinical
    standards for diagnosing intellectual disability, the court’s
    determination that Mr. Hall is not intellectually disabled
    cannot be considered valid”).
    This Court agrees with the medical experts that when a
    defendant’s IQ test score falls within the test’s acknowl­
    edged and inherent margin of error, the defendant must
    be able to present additional evidence of intellectual disa­
    bility, including testimony regarding adaptive deficits.
    It is not sound to view a single factor as dispositive of a
    conjunctive and interrelated assessment. See 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 individuals
    with a lower IQ score”). The Florida statute, as interpreted
    by its courts, misuses IQ score on its own terms; and
    22                    HALL v. FLORIDA
    Opinion of the Court
    this, in turn, bars consideration of evidence that must be
    considered in determining whether a defendant in a capi­
    tal case has intellectual disability. Florida’s rule is invalid
    under the Constitution’s Cruel and Unusual Punishments
    Clause.
    E
    Florida seeks to execute a man because he scored a 71
    instead of 70 on an IQ test. Florida is one of just a few
    States to have this rigid rule. Florida’s rule misconstrues
    the Court’s statements in Atkins that intellectually dis­
    ability is characterized by an IQ of “approximately 
    70.” 536 U.S., at 308
    , n. 3. Florida’s rule is in direct opposition to
    the views of those who design, administer, and interpret
    the IQ test. By failing to take into account the standard
    error of measurement, Florida’s law not only contradicts
    the test’s own design but also bars an essential part of a
    sentencing court’s inquiry into adaptive functioning.
    Freddie Lee Hall may or may not be intellectually dis­
    abled, but the law requires that he have the opportunity to
    present evidence of his intellectual disability, including
    deficits in adaptive functioning over his lifetime.
    The death penalty is the gravest sentence our society
    may impose. Persons facing that most severe sanction
    must have a fair opportunity to show that the Constitution
    prohibits their execution. Florida’s law contravenes our
    Nation’s commitment to dignity and its duty to teach
    human decency as the mark of a civilized world. The
    States are laboratories for experimentation, but those
    experiments may not deny the basic dignity the Constitu­
    tion protects.
    The judgment of the Florida Supreme Court is reversed,
    and the case is remanded for further proceedings not
    inconsistent with this opinion.
    So ordered.
    Cite as: 572 U. S. ____ (2014)            1
    ALITO, J., dissenting
    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 ALITO, with whom THE CHIEF JUSTICE, JUSTICE
    SCALIA, and JUSTICE THOMAS join, dissenting.
    In Atkins v. Virginia, 
    536 U.S. 304
    (2002), the Court
    held that the Eighth Amendment prohibits a death sen­
    tence for defendants who are intellectually disabled but
    does not mandate the use of a single method for identify­
    ing such defendants. Today, the Court overrules the latter
    holding based largely on the positions adopted by private
    professional associations. In taking this step, the Court
    sharply departs from the framework prescribed in prior
    Eighth Amendment cases and adopts a uniform national
    rule that is both conceptually unsound and likely to result
    in confusion. I therefore respectfully dissent.
    I
    The Court’s approach in this case marks a new and most
    unwise turn in our Eighth Amendment case law. In At-
    kins and other cases, the Court held that the prohibition of
    cruel and unusual punishment embodies the “evolving
    standards of decency that mark the progress of a maturing
    society,” and the Court explained that “those evolving
    standards should be informed by objective factors to the
    maximum possible extent.” 
    Id., at 312
    (internal quotation
    marks omitted). In addition, the Court “pinpointed that
    the clearest and most reliable objective evidence of con­
    temporary values is the legislation enacted by the coun­
    2                    HALL v. FLORIDA
    ALITO, J., dissenting
    try’s legislatures.” 
    Ibid. In these prior
    cases, when the Court referred to the
    evolving standards of a maturing “society,” the Court
    meant the standards of American society as a whole. Now,
    however, the Court strikes down a state law based on the
    evolving standards of professional societies, most notably
    the American Psychiatric Association (APA). The Court
    begins its analysis with the views of those associations,
    see ante, at 7–12, and then, after briefly discussing the
    enactments of state legislatures, see ante, at 12–16, re­
    turns to the associations’ views in interpreting Atkins and
    in exercising the Court’s “independent judgment” on the
    constitutionality of Florida’s law, see ante, at 16–22. This
    approach cannot be reconciled with the framework pre­
    scribed by our Eighth Amendment cases.
    A
    Under this Court’s modern Eighth Amendment prece­
    dents, whether a punishment is “cruel and unusual” de­
    pends on currently prevailing societal norms, and the
    Court has long held that laws enacted by state legislatures
    provide the “clearest and most reliable objective evidence
    of contemporary values,” Penry v. Lynaugh, 
    492 U.S. 302
    ,
    331 (1989). This is so because “in a democratic society[,]
    legislatures, not courts, are constituted to respond to the
    will and consequently the moral values of the people,”
    Gregg v. Georgia, 
    428 U.S. 153
    , 175–176 (1976) (joint
    opinion of Stewart, Powell, and Stevens, JJ.) (internal
    quotation marks omitted). Under this approach, as origi­
    nally conceived, the Court first asked whether a chal­
    lenged practice contravened a clear national consensus
    evidenced by state legislation, and only if such a consen­
    sus was found would the Court go on and ask “whether
    there is reason to disagree with [the States’] judgment.”
    
    Atkins, 536 U.S., at 313
    .
    Invoking this two-step procedure, Atkins held that the
    Cite as: 572 U. S. ____ (2014)            3
    ALITO, J., dissenting
    Eighth Amendment forbids the execution of defendants
    who are intellectually disabled. See 
    id., at 315–316.
    Critical to the Court’s analysis was the conclusion that
    “today our society views mentally retarded offenders as
    categorically less culpable than the average criminal.” 
    Id., at 316.
    “This consensus,” the Court continued, “unques­
    tionably reflects widespread judgment about . . . the rela­
    tionship between mental retardation and the penological
    purposes served by the death penalty.” 
    Id., at 317.
       While Atkins identified a consensus against the execu­
    tion of the intellectually disabled, the Court observed that
    there was “serious disagreement” among the States with
    respect to the best method for “determining which offend­
    ers are in fact retarded.” 
    Ibid. The Court therefore
    “le[ft]
    to the States the task of developing appropriate ways” to
    identify these defendants. 
    Ibid. (internal quotation marks
    and alteration omitted). As we noted just five years ago,
    Atkins “did not provide definitive procedural or substan­
    tive guides for determining when a person” is intellectually
    disabled. Bobby v. Bies, 
    556 U.S. 825
    , 831 (2009).
    B
    Consistent with the role that Atkins left for the States,
    Florida follows the procedure now at issue. As we ex­
    plained in Atkins, in order for a defendant to qualify as
    intellectually disabled, three separate requirements must
    be met: It must be shown that a defendant has both
    (1) significantly subaverage intellectual functioning and
    (2) deficits in adaptive behavior, and that (3) the onset of
    both factors occurred before the age of 18. 
    See 536 U.S., at 318
    ; ante, at 8. In implementing this framework, Flor­
    ida has determined that the first requirement cannot be
    satisfied if the defendant scores higher than 70 on IQ
    tests, the long-accepted method of measuring intellectual
    4                         HALL v. FLORIDA
    ALITO, J., dissenting
    functioning.1 The Court today holds that this scheme
    offends the Eighth Amendment. The Court objects that
    Florida’s approach treats IQ test scores as conclusive and
    ignores the fact that an IQ score might not reflect “true”
    IQ because of errors in measurement. The Court then
    concludes that a State must view a defendant’s IQ as a
    range of potential scores calculated using a statistical
    concept known as the “standard error of measurement” or
    SEM. See Part II–B–1, infra. The Court holds that if this
    range includes an IQ of 70 or below (the accepted level for
    intellectual disability), the defendant must be permitted to
    produce other evidence of intellectual disability in addition
    to IQ scores.
    I see no support for this holding in our traditional ap­
    proach for identifying our society’s evolving standards of
    decency. Under any fair analysis of current state laws,
    the same absence of a consensus that this Court found in
    Atkins persists today. It is telling that Hall himself does
    not rely on a consensus among States. He candidly argues
    instead that “the precise number of States that share
    Florida’s approach is immaterial.” Reply Brief 2.
    The Court’s analysis is more aggressive. According to
    the Court, a “significant majority of States” reject Florida’s
    “strict 70 cutoff ” and instead take “the SEM into account”
    when deciding whether a defendant meets the first re­
    quirement of the intellectual-disability test. Ante, at 12,
    16. On the Court’s count, “at most nine States mandate a
    strict IQ score cutoff at 70”; 22 States allow defendants to
    present “additional evidence” when an individual’s test
    ——————
    1 See, e.g., American Association of Intellectual and Developmental
    Disabilities (AAIDD), Intellectual Disability 10–11 (11th ed. 2010)
    (hereinafter AAIDD 11th ed.) (cataloguing history of IQ “cutoff criteria”
    since 1959). Earlier publications of the AAIDD were published under
    its former name, the American Association on Mental Retardation
    (hereinafter AAMR).
    Cite as: 572 U. S. ____ (2014)                     5
    ALITO, J., dissenting
    score is between 70 and 75, ante, at 20;2 and 19 States
    have abolished the death penalty or have long suspended
    its operation. Ante, at 14. From these numbers, the Court
    concludes that “in 41 States” a defendant “with an IQ
    score of 71” would “not be deemed automatically eligible
    for the death penalty.” Ibid.3 This analysis is deeply
    flawed.
    To begin, in addition to the 8 other States that the Court
    recognizes as having rules similar to Florida’s, 1 more,
    Idaho, does not appear to require courts to take the SEM
    into account in rejecting a claim of intellectual disability.4
    And of the remaining 21 States with the death penalty, 9
    have either said nothing about the SEM or have not clari­
    fied whether they require its use.5 Accordingly, of the
    ——————
    2I  assume that by “additional evidence” the Court means evidence
    other than further IQ testing because Florida’s rule already “allows for
    multiple evaluations, and . . . [petitioner] could have sought still more
    testing.” Brief for Respondent 44. See also Brief for Petitioner 50; App.
    107–108.
    3 As I discuss below, the Florida Supreme Court did not base its deci­
    sion on a finding that Hall’s IQ was 71. The Florida courts considered
    several IQ scores, all above 70. See App. 107–108; Brief for Petitioner
    50.
    4 See Idaho Code §19–2515A(1)(b) (Lexis Cum. Supp. 2013); Pizzuto v.
    State, 
    146 Idaho 720
    , 729, 
    202 P.3d 642
    , 651 (2008) (stating that “the
    legislature did not require that the IQ score be within five points of 70
    or below” and giving the District Court discretion to interpret the
    defendant’s IQ).
    5 Montana, New Hampshire, and Wyoming have not ruled on the
    subject. Two States have not defined “significantly subaverage” intel­
    lectual functioning. See Colo. Rev. Stat. Ann. §18–1.3–1101(2) (2013);
    S. C. Code Ann. §16–3–20 (2003 and 2013 Cum. Supp.); Franklin v.
    Maynard, 356 S. C. 276, 278–279, 
    588 S.E.2d 604
    , 605 (2003) (per
    curiam). Two States have statutes that impose rebuttable presump­
    tions of intellectual disability if a defendant’s IQ is below 65 or 70 but
    have not said whether a defendant would be allowed to provide further
    evidence if his IQ were over 70. See Ark. Code Ann. §5–4–618 (2013);
    Neb. Rev. Stat. §28–105.01 (2013 Supp.). One State’s Supreme Court
    mentioned measurement errors but only to explain why a defendant
    6                         HALL v. FLORIDA
    ALITO, J., dissenting
    death-penalty states, 10 (including Florida) do not require
    that the SEM be taken into account, 12 consider the SEM,
    and 9 have not taken a definitive position on this question.
    These statistics cannot be regarded as establishing a
    national consensus against Florida’s approach.
    Attempting to circumvent these statistics, the Court
    includes in its count the 19 States that never impose the
    death penalty, but this maneuver cannot be justified. It is
    true that the Court has counted non-death-penalty States
    in some prior Eighth Amendment cases, but those cases
    concerned the substantive question whether a class of
    individuals should be categorically ineligible for the death
    penalty. In Roper v. Simmons, 
    543 U.S. 551
    (2005), for
    example, the Court counted non-death-penalty States as
    part of the consensus against the imposition of a capital
    sentence for a crime committed by a minor. 
    Id., at 574.
    The Court reasoned that a State’s decision to abolish the
    death penalty necessarily “demonstrates a judgment that
    the death penalty is inappropriate for all offenders, includ­
    ing juveniles.” 
    Ibid. No similar reasoning
    is possible here. The fact that a
    State has abolished the death penalty says nothing about
    how that State would resolve the evidentiary problem of
    identifying defendants who are intellectually disabled. As
    I explain below, a State may reasonably conclude that
    Florida’s approach is fairer than and just as accurate as
    the approach that the Court now requires, and therefore it
    cannot be inferred that a non-death-penalty State, if
    forced to choose between the two approaches, would neces­
    sarily select the Court’s. For all these reasons, it is quite
    ——————
    must prove deficits in adaptive behavior despite having an IQ below 70.
    See Stripling v. State, 
    261 Ga. 1
    , 3, 
    401 S.E.2d 500
    , 504 (1991).
    Another State’s Supreme Court mentioned the SEM in responding to
    an argument by the defendant, but it did not suggest that the SEM was
    legally relevant. See Goodwin v. State, 
    191 S.W.3d 20
    , 30–31, and n. 7
    (Mo. 2006).
    Cite as: 572 U. S. ____ (2014)                  7
    ALITO, J., dissenting
    wrong for the Court to proclaim that “the vast majority of
    States” have rejected Florida’s approach. Ante, at 16.
    Not only are the States divided on the question whether
    the SEM should play a role in determining whether a
    capital defendant is intellectually disabled, but the States
    that require consideration of the SEM do not agree on the
    role that the SEM should play. Those States differ, for
    example, on the sort of evidence that can be introduced
    when IQ testing reveals an IQ over 70. Some require
    further evidence of intellectual deficits, while others per­
    mit the defendant to move on to the second prong of the
    test and submit evidence of deficits in adaptive behavior.6
    The fairest assessment of the current situation is that the
    States have adopted a multitude of approaches to a very
    difficult question.
    In light of all this, the resolution of this case should be
    straightforward: Just as there was no methodological
    consensus among the States at the time of Atkins, there is
    no such consensus today. And in the absence of such a
    consensus, we have no basis for holding that Florida’s
    method contravenes our society’s standards of decency.
    C
    Perhaps because it recognizes the weakness of its argu­
    ments about a true national consensus, the Court places
    heavy reliance on the views (some only recently an­
    nounced) of professional organizations, but the Court
    attempts to downplay the degree to which its decision is
    dependent upon the views of these private groups. In a
    game attempt to shoehorn the views of these associations
    into the national-consensus calculus, the Court reasons as
    follows. The views of these associations, the Court states,
    help in determining “how [IQ] scores relate to the holding
    ——————
    6 Compare Ybarra v. State, 127 Nev. ___, ___, 
    247 P.3d 269
    , 274
    (2011), with State v. Dunn, 2001–1635, pp. 25–26 (La. 5/11/10), 
    41 So. 3d
    454, 470.
    8                       HALL v. FLORIDA
    ALITO, J., dissenting
    in Atkins”; “[t]his in turn leads to a better understanding
    of how the legislative policies of various States, and the
    holdings of state courts, implement the Atkins rule”; and
    “[t]hat understanding informs our determination whether
    there is a consensus that instructs how to decide the spe­
    cific issue presented here.” Ante, at 7.
    I cannot follow the Court’s logic. Under our modern
    Eighth Amendment cases, what counts are our society’s
    standards—which is to say, the standards of the American
    people—not the standards of professional associations,
    which at best represent the views of a small professional
    elite.
    The Court also mistakenly suggests that its methodol­
    ogy is dictated by Atkins. See ante, at 16–19. On the con-
    trary, Atkins expressly left “to the States” the task of
    defining intellectual disability. And although the Atkins
    Court perceived a “professional consensus” about the best
    procedure to be used in identifying the intellectually dis­
    abled, the Atkins Court declined to import that view into
    the 
    law. 536 U.S., at 316
    , n. 21. Instead, the Court made
    clear that this professional consensus was “by no means
    dispositive.” 
    Id., at 317,
    n. 21; see 
    id., at 317,
    and n. 22.
    D
    The Court’s reliance on the views of professional associ­
    ations will also lead to serious practical problems. I will
    briefly note a few.
    First, because the views of professional associations
    often change,7 tying Eighth Amendment law to these
    views will lead to instability and continue to fuel pro­
    tracted litigation. This danger is dramatically illustrated
    by the most recent publication of the APA, on which the
    Court relies. This publication fundamentally alters the
    ——————
    7 See Forensic Psychology and Neuropsychology for Criminal and
    Civil Cases 57 (H. Hall ed. 2008) (hereinafter Forensic Psychology).
    Cite as: 572 U. S. ____ (2014)                  9
    ALITO, J., dissenting
    first prong of the longstanding, two-pronged definition of
    intellectual disability that was embraced by Atkins and
    has been adopted by most States. In this new publication,
    the APA discards “significantly subaverage intellectual
    functioning” as an element of the intellectual-disability
    test.8 Elevating the APA’s current views to constitutional
    significance therefore throws into question the basic ap­
    proach that Atkins approved and that most of the States
    have followed.
    It is also noteworthy that changes adopted by profes­
    sional associations are sometimes rescinded. For example,
    in 1992 the AAIDD extended the baseline “intellectual
    functioning cutoff ” from an “IQ of 70 or below” to a “score
    of approximately 70 to 75 or below.” AAIDD 11th ed. 10
    (Table 1.3) (boldface deleted); see 2 Kaplan & Sadock’s
    Comprehensive Textbook of Psychiatry 3449 (B. Sadock,
    V. Sadock, & P. Ruiz eds., 9th ed. 2009) (hereinafter
    Kaplan & Sadock’s). That change “generated much con­
    troversy; by 2000, “only 4 states used the 1992 AAIDD
    definition, with 44 states continuing to use the 1983 defi­
    nition.” 
    Ibid. And in the
    2002 AAIDD, the baseline “IQ
    cut-off was changed” back to approximately “70 or less.”
    
    Ibid. Second, the Court’s
    approach implicitly calls upon the
    Judiciary either to follow every new change in the think­
    ing of these professional organizations or to judge the
    validity of each new change. Here, for example, the Court
    tacitly makes the judgment that the diagnostic criteria for
    intellectual disability that prevailed at the time when
    Atkins was decided are no longer legitimate. The publica­
    tions that Atkins cited differ markedly from more recent
    ——————
    8 Compare   APA, Diagnostic and Statistical Manual of Mental Disor­
    ders 39, 41, 42 (rev. 4th ed. 2000) (hereinafter DSM–IV–TR), with APA,
    Diagnostic and Statistical Manual of Mental Disorders 33, 809 (5th
    ed. 2013) (hereinafter DSM–5).
    10                   HALL v. FLORIDA
    ALITO, J., dissenting
    editions now endorsed by the Court. 
    See 536 U.S., at 308
    ,
    n. 3.
    Third, the Court’s approach requires the Judiciary to
    determine which professional organizations are entitled to
    special deference. And what if professional organizations
    disagree? The Court provides no guidance for deciding
    which organizations’ views should govern.
    Fourth, the Court binds Eighth Amendment law to
    definitions of intellectual disability that are promulgated
    for use in making a variety of decisions that are quite
    different from the decision whether the imposition of a
    death sentence in a particular case would serve a valid
    penological end. In a death-penalty case, intellectual
    functioning is important because of its correlation with the
    ability to understand the gravity of the crime and the
    purpose of the penalty, as well as the ability to resist a
    momentary impulse or the influence of others. See 
    id., at 318,
    320. By contrast, in determining eligibility for social
    services, adaptive functioning may be much more im­
    portant. Cf. DSM–IV–TR, at xxxvii (clinical “considera­
    tions” may not be “relevant to legal judgments” that turn
    on “individual responsibility”); DSM–5, at 20 (similar).
    Practical problems like these call for legislative judg­
    ments, not judicial resolution.
    II
    Because I find no consensus among the States, I would
    not independently assess the method that Florida has
    adopted for determining intellectual disability. But even
    if it were appropriate for us to look beyond the evidence of
    societal standards, I could not conclude that Florida’s
    method is unconstitutional. The Court faults Florida for
    “tak[ing] an IQ score as final and conclusive evidence of a
    defendant’s intellectual capacity” and for failing to recog­
    nize that an IQ score may be imprecise. Ante, at 10. In
    my view, however, Florida has adopted a sensible stand­
    Cite as: 572 U. S. ____ (2014)                     11
    ALITO, J., dissenting
    ard that comports with the longstanding belief that IQ
    tests are the best measure of intellectual functioning. And
    although the Court entirely ignores this part of the Florida
    scheme, the State takes into account the inevitable risk of
    testing error by permitting defendants to introduce multi­
    ple scores.
    In contrast, the Court establishes a standard that
    conflates what have long been understood to be two inde-
    pendent requirements for proving intellectual disability:
    (1) significantly subaverage intellectual functioning and
    (2) deficits in adaptive behavior. The Court also mandates
    use of an alternative method of dealing with the risk of
    testing error without any hint that it is more accurate
    than Florida’s approach.
    A
    1
    The first supposed error that the Court identifies is that
    Florida “takes an IQ score” as “conclusive evidence” of
    intellectual functioning. Ante, at 10. As an initial matter,
    one would get the impression from reading the Court’s
    opinion that Hall introduced only one test score (of 71).
    See ante, at 14. In truth, the Florida courts considered
    multiple scores, all above 70, on the particular IQ test that
    Hall has dubbed the “gold standard.” See Brief for Peti­
    tioner 50; App. 107–108.9 Florida’s statute imposes no
    limit on the number of IQ scores that a defendant may
    introduce, so the Court is simply wrong to analyze the
    Florida system as one that views a single IQ score above
    70 as “final and conclusive evidence” that a defendant does
    not suffer from subaverage intellectual functioning. See
    ——————
    9 See Brief for Petitioner 50 (listing his valid IQ scores of 71, 72, 73,
    and 80). Hall alleges that he also scored a 69 on a Wechsler test, but
    that score was not admitted into evidence because of doubts about its
    validity. App. 107. Hall does not allege that any potential “practice
    effect” skewed his scores.
    12                          HALL v. FLORIDA
    ALITO, J., dissenting
    Brief for Respondent 44 (“Florida’s Rule allows for multi­
    ple evaluations, and if Hall believed a statistical error rate
    prevented any of his tests from reflecting his true score, he
    could have sought still more testing”).
    The proper question to ask, therefore, is whether Flor­
    ida’s actual approach falls outside the range of discretion
    allowed by Atkins. The Court offers no persuasive reason
    for concluding that it does. Indeed, the Court’s opinion
    never identifies what other evidence of intellectual func­
    tioning it would require Florida to admit. As we recog­
    nized in Atkins, the longstanding practices of the States,
    and at least the previous views of professional organiza­
    tions, seem to reflect the understanding that IQ scores are
    the best way to measure intellectual functioning. 
    See 536 U.S., at 316
    .10 Until its most recent publication, the APA,
    for example, ranked the severity of intellectual disability
    exclusively by IQ scores, necessarily pinpointing the onset
    of the disability according to IQ. See DSM–IV–TR, at 42.
    We have been presented with no solid evidence that the
    longstanding reliance on multiple IQ test scores as a
    measure of intellectual functioning is so unreasonable or
    outside the ordinary as to be unconstitutional. The Court
    has certainly not supplied any such information.
    2
    If the Court had merely held that Florida must permit
    defendants to introduce additional evidence (whatever
    that might be) of significantly subaverage intellectual
    ——————
    10 See AAIDD 11th ed. 10 (cataloguing history of IQ “cutoff criteria”
    since 1959); DSM–IV–TR, at 39 (“Mental Retardation” is “characterized
    by significantly subaverage intellectual functioning (an IQ of approxi­
    mately 70 or below) . . .” (boldface deleted)); 
    id., at 41
    (“General intellec­
    tual functioning is defined by the intelligence quotient . . .” (italics
    deleted)); AAMR, Mental Retardation 14 (10th ed. 2002) (hereinafter
    AAMR 10th ed.) (“[I]ntellectual functioning is still best represented by
    IQ scores . . .”).
    Cite as: 572 U. S. ____ (2014)                  13
    ALITO, J., dissenting
    functioning, its decision would be more limited in scope.
    But as I understand the Court’s opinion, it also holds that
    when IQ tests reveal an IQ between 71 and 75, defendants
    must be allowed to present evidence of deficits in adaptive
    behavior—that is, the second prong of the intellectual­
    disability test. See ante, at 9–10, 12, 20. That is a re­
    markable change in what we took to be a universal under­
    standing of intellectual disability just 12 years ago.
    In Atkins, we instructed that “clinical definitions of
    mental retardation require not only [(1)] subaverage intel­
    lectual functioning, but also [(2)] significant limitations in
    adaptive 
    skills.” 536 U.S., at 318
    (emphasis and altera­
    tions added). That is the approach taken by the vast
    majority of States.11 As the Court correctly recognizes,
    most States require “concurrent deficits” in intellectual
    functioning and adaptive behavior, requiring defendants
    to prove both. Ante, at 8 (emphasis added).12
    Yet the Court now holds that when a defendant’s IQ
    score is as high as 75, a court must “consider factors indi­
    cating whether the person has deficits in adaptive func­
    tioning.” Ante, at 12; see ante, at 9–10, 20. In other
    words, even when a defendant has failed to show that he
    meets the first prong of the well-accepted standard for
    intellectual disability (significantly subaverage intellec­
    tual functioning), evidence of the second prong (deficits in
    adaptive behavior) can establish intellectual disability.
    The Court offers little explanation for this sea change.
    ——————
    11 See, e.g., Del. Code Ann., Tit. 11, §4209 (2007); Idaho Code §19–
    2515A; Nev. Rev. Stat. §174.098 (2013); Va. Code Ann. §19.2–264.3:1.1
    (Lexis Cum. Supp. 2013).
    12 The longstanding views of professional organizations have also
    been that intellectual functioning and adaptive behavior are independ­
    ent factors. See, e.g., DSM–IV–TR, at 39. These organizations might
    recommend examining evidence of adaptive behavior even when an IQ
    is above 70, but that sheds no light on what the legal rule should be
    given that most States appear to require defendants to prove each
    prong separately by a preponderance of the evidence.
    14                    HALL v. FLORIDA
    ALITO, J., dissenting
    It asserts vaguely that “[i]t is not sound to view a single
    factor as dispositive of a conjunctive and interrelated
    assessment.” Ante, at 21. But the Court ignores the fact
    that deficits in adaptive behavior cannot be used to estab­
    lish deficits in mental functioning because the two prongs
    are meant to show distinct components of intellectual
    disability. “[I]ntellectual functions” include “reasoning,
    problem solving, planning, abstract thinking, judgment,
    academic learning, and learning from experience,” while
    adaptive functioning refers to the ability “to meet devel­
    opmental and sociocultural standards for personal inde­
    pendence and social responsibility.”          DSM–5, at 33.
    Strong evidence of a deficit in adaptive behavior does not
    necessarily demonstrate a deficit in intellectual function­
    ing. And without the latter, a person simply cannot be
    classified as intellectually disabled.
    It is particularly troubling to relax the proof require­
    ments for the intellectual-functioning prong because that
    is the prong that most directly relates to the concerns that
    led to our primary holding in Atkins. There, we explained
    that “the diminished ability to understand and process
    information, to learn from experience, to engage in logical
    reasoning, or to control impulses”—i.e., diminished intel-
    lectual functioning—“make it less likely that [a defendant]
    can process the information of the possibility of execution
    as a penalty” and therefore be deterred from committing
    
    murders. 536 U.S., at 320
    ; see also 
    id., at 318
    (“[T]hey
    often act on impulse rather than pursuant to a premedi­
    tated plan . . .”); see also ante, at 6. A defendant who does
    not display significantly subaverage intellectual function­
    ing is therefore not among the class of defendants we
    identified in Atkins.
    Finally, relying primarily on proof of adaptive deficits
    will produce inequities in the administration of capital
    punishment. As far as I can tell, adaptive behavior is a
    malleable factor without “firm theoretical and empirical
    Cite as: 572 U. S. ____ (2014)            15
    ALITO, J., dissenting
    roots.” See 2 Kaplan & Sadock’s 3448. No consensus
    exists among States or medical practitioners about what
    facts are most critical in analyzing that factor, and its
    measurement relies largely on subjective judgments.
    Florida’s approach avoids the disparities that reliance on
    such a factor tends to produce. It thus promotes con­
    sistency in the application of the death penalty and confi­
    dence that it is not being administered haphazardly.
    B
    The Court’s second “interrelated” objection to Florida’s
    rule is that it fails to account for the risk of error inherent
    in IQ testing. In order to diminish this risk, the Court
    establishes a rule that if IQ testing reveals an IQ between
    71 and 75, a claim of intellectual disability cannot be
    rejected on the basis of test scores alone. Ante, at 20. The
    Court both misunderstands how the SEM works and fails
    to explain why Florida’s method of accounting for the risk
    of error (allowing a defendant to take and rely on multiple
    tests) is not as effective as the approach that the Court
    compels.
    1
    The Court begins with the simple and uncontroversial
    proposition that every testing situation is susceptible to
    error and thus may result in an imperfect measurement of
    “true” IQ. The Court then wades into technical matters
    that must be understood in order to see where the Court
    goes wrong.
    There are various ways to account for error in IQ test­
    ing. One way is Florida’s approach (evaluate multiple test
    results). Another is to use a mathematical measurement
    called the “standard error of measurement” or SEM. See
    AAMR 10th ed. 67–71 (App. 4.1). Of critical importance,
    there is not a single, uniform SEM across IQ tests or even
    across test-takers. Rather, “the [SEM] varies by test,
    16                    HALL v. FLORIDA
    ALITO, J., dissenting
    subgroup, and age group.” User’s Guide To Accompany
    AAIDD 11th ed.: Definition, Classification, and Systems of
    Supports 22 (2012).
    Once we know the SEM for a particular test and a par­
    ticular test-taker, adding one SEM to and subtracting one
    SEM from the obtained score establishes an interval of
    scores known as the 66% confidence interval. See AAMR
    10th ed. 57. That interval represents the range of scores
    within which “we are [66%] sure” that the “true” IQ falls.
    See Oxford Handbook of Child Psychological Assessment
    291 (D. Saklofske, C. Reynolds, & V. Schwean eds. 2013).
    The interval is centered on the obtained score, and it
    includes scores that are above and below that score by the
    amount of the SEM. Since there is about a 66% chance
    that the test-taker’s “true” IQ falls within this range, there
    is about a 34% chance that the “true” IQ falls outside the
    interval, with approximately equal odds that it falls above
    the interval (17%) or below the interval (17%).
    An example: If a test-taker scores a 72 on an IQ test
    with a SEM of 2, the 66% confidence interval is the range
    of 70 to 74 (72 ± 2). In this situation, there is approxi­
    mately a 66% chance that the test-taker’s “true” IQ is
    between 70 and 74; roughly a 17% chance that it is above
    74; and roughly a 17% chance that it is 70 or below. Thus,
    there is about an 83% chance that the score is above 70.
    Similarly, using two SEMs, we can build a 95% confi­
    dence interval. The process is the same except that we
    add two SEMs to and subtract two SEMS from the ob­
    tained score. To illustrate the use of two SEMs, let us
    hypothesize a case in which the defendant’s obtained score
    is 74. With the same SEM of 2 as in the prior example,
    there would be a 95% chance that the true score is be­
    tween 70 and 78 (74 ± 4); roughly a 2.5% chance that the
    score is above 78; and about a 2.5% chance that the score
    is 70 or below. The probability of a true score above 70
    would be roughly 97.5%. As these two examples show, the
    Cite as: 572 U. S. ____ (2014)           17
    ALITO, J., dissenting
    greater the degree of confidence demanded, the greater
    the range of scores that will fall within the confidence
    interval and, therefore, the further away from 70 an ob­
    tained score could be and yet still have 70 fall within its
    confidence interval.
    2
    The Court misunderstands these principles and makes
    factual mistakes that will surely confuse States attempt­
    ing to comply with its opinion.
    First, the Court unjustifiably assumes a blanket (or very
    common) error measurement of 5. See ante, at 20. That
    assumption gives rise to the Court’s holding that a de­
    fendant must be permitted to introduce additional evi­
    dence when IQ tests reveal an IQ as high as 75. See 
    ibid. SEMs, however, vary
    by IQ test and test-taker, and there
    is no reason to assume a SEM of 5 points; indeed, it ap­
    pears that the SEM is generally “estimated to be three to
    five points” for well-standardized IQ tests. AAMR 10th ed.
    57. And we know that the SEM for Hall’s most recent IQ
    test was 2.16—less than half of the Court’s estimate of 5.
    Brief for Petitioner 40, n. 17.
    Relatedly, the Court misreads the authorities on which
    it relies to establish this cutoff IQ score of 75. It is true
    that certain professional organizations have advocated a
    cutoff of 75 and that Atkins cited those organizations’
    cutoff. See ante, at 12, 20. But the Court overlooks a
    critical fact: Those organizations endorsed a 75 IQ cutoff
    based on their express understanding that “one standard
    error of measurement [SEM]” is “three to five points for
    well-standardized” IQ tests. AAMR, Mental Retardation
    37 (9th ed. 1992) (hereinafter AAMR 9th ed.); Atkins, 536
    U. S., 309, n. 5 (citing AAMR 9th ed.; 2 Kaplan & Sadock’s
    2592 (B. Sadock & V. Sadock eds., 7th ed. 2000)); see also
    AAMR 10th ed. 57; AAIDD 11th ed. 36. In other words,
    the number 75 was relevant only to the extent that a
    18                    HALL v. FLORIDA
    ALITO, J., dissenting
    single SEM was “estimated” to be as high as 5 points.
    AAMR 9th ed. 37. Here, by contrast, we know that the
    SEM for Hall’s latest IQ test was less than half of that
    estimate; there is no relevance to the number 75 in this
    case. To blindly import a five-point margin of error when
    we know as a matter of fact that the relevant SEM is 2.16
    amounts to requiring consideration of more than two
    SEMs—an approach that finds no support in Atkins or
    anywhere else.
    Because of these factual errors and ambiguities, it is
    unclear to me whether the Court concludes that a defend­
    ant is constitutionally entitled to introduce non-test evi­
    dence of intellectual disability (1) whenever his score is 75
    or lower, on the mistaken understanding that the SEM for
    most tests is 5; (2) when the 66% confidence interval
    (using one SEM) includes a score of 70; or (3) when the
    95% confidence interval (using two SEMs) includes a score
    of 70. In my view, none of these approaches is defensible.
    An approach tied to a fixed score of 75 can be dismissed
    out of hand because, as discussed, every test has a differ­
    ent SEM.
    The other two approaches would require that a defend­
    ant be permitted to submit additional evidence when his
    IQ is above 70 so long as the 66% or 95% confidence inter­
    val (using one SEM or two SEMs, respectively) includes a
    score of 70, but there is no foundation for this in our
    Eighth Amendment case law. As Hall concedes, the
    Eighth Amendment permits States to assign to a defend­
    ant the burden of establishing intellectual disability by at
    least a preponderance of the evidence. See Tr. of Oral Arg.
    12. In other words, a defendant can be required to prove
    that the probability of a 70 or sub-70 IQ is greater than
    50%. Under the Court’s approach, by contrast, a defend­
    ant could prove significantly subaverage intellectual func­
    tioning by showing simply that the probability of a “true”
    IQ of 70 or below is as little as 17% (under a one-SEM
    Cite as: 572 U. S. ____ (2014)                 19
    ALITO, J., dissenting
    rule) or 2.5% (under a two-SEM rule). This totally trans­
    forms the allocation and nature of the burden of proof.
    I have referred to the 66% and 95% confidence intervals
    only because they result from the most straightforward
    application of the SEM in this context: One SEM estab­
    lishes the 66% confidence interval; two SEMs establish the
    95% confidence interval. See AAIDD 11th ed. 36. But it
    would be simple enough to devise a 51% confidence inter­
    val—or a 99% confidence interval for that matter. There
    is therefore no excuse for mechanically imposing stand­
    ards that are unhinged from legal logic and that over-
    ride valid state laws establishing burdens of proof. The
    appropriate confidence level is ultimately a judgment best
    left to legislatures, and their judgment has been that a
    defendant must establish that it is more likely than not
    that he is intellectually disabled. I would defer to that
    determination.
    3
    The Court also fails to grasp that Florida’s system al­
    ready accounts for the risk of testing error by allowing the
    introduction of multiple test scores. The Court never
    explains why its criticisms of the uncertainty resulting
    from the use of a single IQ score apply when a defendant
    consistently scores above 70 on multiple tests. Contrary to
    the Court’s evident assumption, the well-accepted view is
    that multiple consistent scores establish a much higher
    degree of confidence.13
    ——————
    13 See Oxford Handbook of Child Psychological Assessment 291
    (D. Saklofske, C. Reynolds, & V. Schwean eds. 2013) (multiple scores
    provide “greater precision”); A. Frances, Essentials of Psychiatric
    Diagnosis: Responding to the Challenge of DSM–5, p. 31 (rev. ed. 2013)
    (“The pattern of test scores is more important than the score on any
    given test”). When there are multiple scores, moreover, there is good
    reason to treat low scores differently from high scores: “Although one
    cannot do better on an IQ test than one is capable of doing, one can
    certainly do worse.” Forensic Psychology 56. (“[A] sharp, unexplained
    20                        HALL v. FLORIDA
    ALITO, J., dissenting
    The Court’s only attempt to address this is to say that
    “the analysis of multiple IQ scores jointly is a complicated
    endeavor,” ante, at 11, but any evaluation of intellectual
    disability, whether based on objective tests or subjective
    observations, is “complicated.” If conducting the proper
    analysis of multiple scores produces an IQ as reliable as
    the approach mandated by the Court, there is no basis for
    rejecting Florida’s approach.14
    *    *     *
    For these reasons, I would affirm the judgment of the
    Florida Supreme Court.
    ——————
    drop in IQ scores following incarceration can be strong evidence of
    malingering”); 
    Frances, supra, at 31
    (“[H]igher scores are likely to be
    the more indicative, since there are many reasons why a given score
    might underestimate a person’s intelligence, but no reason why scores
    should overestimate it”).
    14 The Court also states that because IQ testing itself may be flawed,
    “multiple examinations may result in repeated similar scores” that are
    “not conclusive evidence of intellectual functioning.” Ante, at 12. That
    argument proves too much: If potential flaws in administering multiple
    tests are sufficient to render them inaccurate, the Court should con­
    clude that even scores of 90 or 100 are not sufficient. The appropriate
    remedy for incorrectly administered tests is for a court to disregard
    those tests, not to ignore the well-established fact that multiple, prop-
    erly administered tests yielding scores above 70 can give a high degree
    of confidence that an individual is not intellectually disabled.