(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.
