In 2002, in Atkins v. Virginia, the Supreme Court prohibited capital punishment for defendants who suffered from what the Court then called “mental retardation.” However, the Court did not prescribe any particular process or standards for determining which defendants qualify. Florida adopted a particularly restrictive approach, refusing even to consider the full spectrum of evidence of intellectual limitations if a defendant’s IQ had not been scored 70 or lower. Earlier this week, in Hall v. Florida, the Supreme Court rejected this test for failing to take into account the standard error of measurement (SEM) of IQ tests. “This rigid rule,” Justice Kennedy wrote for a narrow 5-4 majority, “creates an unacceptable risk that persons with intellectual disability will be executed, and thus is unconstitutional.” (Along the way, the Court expressly changed its preferred terminology from “mental retardation” to “intellectual disability.”)
Kennedy’s reference to “unacceptable risk” goes to the heart of the disagreement between the majority and the dissenters.
In short, the majority sought to minimize the risk of what we might refer to as “false positives,” that is, erroneous decisions to execute defendants who actually have the culpability-diminishing deficits that were of concern in Atkins. By contrast, the dissenters seemed about equally concerned with “false negatives,” that is, erroneous decisions not to execute defendants who lack the Atkins deficits.
Consistent with established professional opinion, both sides in Hall recognized that intellectual disability should be assessed by reference 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. . . .
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.” (8, citations omitted).
IQ tests are commonly used by psychological experts to help determine whether the intellectual functioning criterion is satisfied, with a score of 70 recognized as an important benchmark.
Under the Florida approach, however, the score of 70 became a dispositive threshold test: if the defendant could not present a valid score of 70 or lower, then no evidence of deficits in adaptive functioning could be considered, no matter how compelling.
In the Court’s view, Florida gave too much weight to the IQ score in isolation from adaptive functioning evidence:
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. (9-10)
Thus, where there is any real possibility that a defendant’s intellectual functioning is significantly subaverage, the Court wants the defendant’s adaptive deficits also to be considered. The Court gave this idea more concrete meaning by reference to SEM. “Each IQ test has a ‘standard error of measurement’ . . . . A test’s SEM is a statistical fact, a reflection of the inherent imprecision of the test itself” (10). “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” (11, citation omitted).
The Court concluded that an IQ score of 75 or lower should entitle the defendant to present additional evidence of intellectual disability. Although the calculation of this figure is not entirely clear in the Court’s opinion, it appears to be based on the 2 SEM range from 70. In other words, the Court seems to be trying to require 95% certainty that a defendant’s “true” IQ is above 70 before shutting down further analysis.
To Justice Alito, writing for the dissenters, this calculus was nonsensical. After all, in theory, the defendant bears the burden of proving the Atkins defense by a preponderance of the evidence. Rigorously applied, this principle should cause the defendant to lose if there is even a 50% chance that he lacks “significantly subaverage intellectual functioning.” Yet, the Court’s approach seems to permit the defendant to proceed with the Atkins defense if there is even a 5% chance that his true IQ is 70 or lower.
To be sure, an IQ of 75 does not necessarily mean that the defendant wins; this merely permits the defendant to present evidence of poor adaptive functioning. Once the judge has all of the evidence, the judge may still conclude that the deficits in adaptive functioning are not enough to make up for a “high” IQ score.
Yet, in the dissenters’ view, there are particular reasons to think that lower-court judges will be led astray by the softer adaptive functioning evidence. As Justice Alito put it,
As far as I can tell, adaptive behavior is a malleable factor without “firm theoretical and empirical roots.” 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. (14-15, citation omitted)
Alito is evidently focused on the risk of false negatives–incorrect determinations that a particular defendant cannot be executed under Atkins. A straight preponderance test, which he would seemingly prefer, would more-or-less equalize the risks of false positives and false negatives.
The majority takes a more protective approach. They are willing to accept that some defendants whose true IQ is above 70 will get the benefit of Atkins as the price of saving from execution those whose IQ scores really are erroneously high.
We should not be surprised to see aligned with Kennedy those Justices who originally voted for Atkins and who generally seem to have a skeptical view of capital punishment. Nor should we be surprised to see aligned with Alito those Justices who originally voted against Atkins and who generally have a more supportive view of capital punishment.
Hall fits well with what seems to be Kennedy’s (and the Court’s) general approach to capital punishment over the past dozen years: do not directly challenge the constitutionality of the death penalty, but insist with increasing rigor that this most severe punishment be reserved for those defendants who, in terms of culpability, can be said with confidence to be truly the worst of the worst.