Hall v. Florida
572 US ___ (2014)

Annotate this Case

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, Washington, 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

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No. 12–10882

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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 foreclosed. 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 newlywed. 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 attempted to apprehend them. Hall received the death penalty for both murders, although his sentence for the Coburn murder was later reduced on account of insufficient evidence of premeditation. Hall v. Florida, 403 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 opinion uses the term “intellectual disability” to describe the identical phenomenon. See Rosa’s Law, 124Stat. 2643 (changing entries in the U. S. Code from “mental retardation” to “intellectual disability”); Schalock et. al, The Renaming of Mental Retardation: Understanding the Change to the Term Intellectual Disability, 45 Intellectual & Developmental Disabilities 116 (2007). This change in terminology 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 Statistical 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 –399 (1987), Hall was resentenced. Hall then presented substantial and unchallenged evidence of intellectual disability. School records indicated that his teachers 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 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 ability 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 adaptive functioning all the more severe. Hall was raised—in the words of the sentencing judge—“under the most horrible family circumstances imaginable.” Id., at 53. Al-though “[t]eachers and siblings alike immediately recognized [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 himin the sand up to his neck to ‘strengthen his legs,’ ” and “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 convenience 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 retardation, 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 sentenced to death. The Florida Supreme Court affirmed, concluding that “Hall’s argument that his mental retardation 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 disability. Atkins v. Virginia, 536 U. S., at 321. On November 30, 2004, Hall filed a motion claiming that he had intellectual disability and could not be executed. More than five years later, Florida held a hearing to consider Hall’s motion. Hall again presented evidence of intellectual disability, including an IQ test score of 71. (Hall had received 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 because 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 Fourteenth Amendment applies those restrictions to the States. Roper v. Simmons, 543 U. S. 551, 560 (2005) ; Furman v. Georgia, 408 U. S. 238 –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 enlightened 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 “evolving standards of decency that mark the progress of a maturing society.” Trop, supra, at 101. The Eighth 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 engage 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 values are also ill-served by executing those with intellectual disability. The diminished capacity of the intellectually disabled lessens moral culpability and hence the retributive value of the punishment. See id., at 319 (“If the culpability 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, receive 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, implement 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 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 Psychological 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 adaptive 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 concurrently 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 “significantly 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 population. 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 deviation 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 measurement error in the calculation. But the Florida Supreme 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 faculties 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 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 authorities 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 individuals 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 Intelligence 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) (identifying 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 examiner’s demeanor; the subjective judgment involved in scoring certain questions on the exam; and simple lucky guessing. See American Association on Intellectual and Developmental 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 intellectual functioning cannot be reduced to a single numerical 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 reflect 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 measurement 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 groupings; these scores are similar, but not identical, often due to sampling error)”). Even when a person has taken multiple 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 Assessment 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, 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 protections 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. Commonwealth, 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 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 interpreted, however. See, e.g., State v. Vela, 279 Neb. 94, 126, 137, 777 N. W. 2d 266, 292, 299 (2010) (Although Nebraska’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 principal 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, 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 practiceis 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 decade, 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 Oregon, 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 positioncould not be executed even without a finding of intellectual disability. Thus in 41 States an individual in Hall’sposition—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 considerations bearing on a determination of consensus. Consistency of the direction of change is also relevant. See id., at565–566 (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 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 defendants to present additional evidence of intellectual disability when their IQ test score is above 70.

     Since Atkins, five States have abolished the death penalty through legislation. See 2012 Conn. Pub. Acts no. 12–5; Ill. Comp. Stat. ch. 725, §119–1 (West 2012); Md. Correc. 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 additional 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 inferences 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 strict cutoff at 70. Cf. Roper, supra, at 566 (“Since Stanford v. Kentucky, 492 U. S. 361 (1989) , no State that previously 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 Legislature, which passed the relevant legislation prior to Atkins, might well have believed that its law would not createa fixed cutoff at 70. The staff analysis accompanyingthe 2001 bill states that it “does not contain a set IQlevel . . . .  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 evidence 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. Wainwright with regard to insanity, ‘we leave to the State[s] the task of developing appropriate ways to enforce the constitutional restriction upon [their] execution of sentences.’ ” 536 U. S., at 317 (quoting Ford v. Wainwright, 477 U. S. 399 –417 (1986); citation omitted).

As discussed above, the States play a critical role in advancing protections and providing the Court with information that contributes to an understanding of how intellectual 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 Diagnostic 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. Furthermore, 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 intellectual disability “by definition . . . have diminished capacities to understand and process information, to communicate, 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 measurement of approximately five points; hence, an IQ of 70 is considered to represent a band or zone of 65 to 75. Treating 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 Respondent 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 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 statute, 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 framework. Atkins itself points to the diagnostic criteria employed 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 situations and mastery of practical tasks.” DSM–5, at 37. This statement well captures the Court’s independent assessment 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 approximation, not a final and infallible assessment of intellectual functioning. See APA Brief 24 (“[I]t is standard pyschometric practice to report the ‘estimates of relevant reliabilities 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 measurement”). SEM is not a concept peculiar to the psychiatric profession and IQ tests. It is a measure that is recognized 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 importance when conducting the conjunctive assessment necessary to assess an individual’s intellectual ability. See American Association on Intellectual and Developmental 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 represents a range rather than a fixed number. A State that ignores the inherent imprecision of these tests risks executing 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 acknowledged and inherent margin of error, the defendant must be able to present additional evidence of intellectual disability, 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; andthis, in turn, bars consideration of evidence that must be considered in determining whether a defendant in a capital 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.” 536U. 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 topresent 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 Constitution 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.

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