explaining that “the term ‘significantly subaverage’ has been used by [intellectual disability] professionals to describe the level of impairment found in, individuals whose performance on standardized intelligence tests places them two standard deviations below the mean; that is, in the lowest two,and a half or three percent of the population”
How later courts described this case
- explaining that “the term ‘significantly subaverage’ has been used by [intellectual disability] professionals to describe the level of impairment found in, individuals whose performance on standardized intelligence tests places them two standard deviations below the mean; that is, in the lowest two,and a half or three percent of the population”
- finding that mental retardation is not measured according to a fixed intelligence test score but constitutes an assessment of overall capacity based on a consideration of all relevant evidence
- observing that IQ test scores are not precise due to measurement error, and holding that mental retardation should not be determined according to a fixed IQ cut score, but upon an assessment of the defendant’s overall capacity based on a consideration of all relevant evidence
- providing that post-conviction claims of execution 1 setting forth the factual basis for a finding of significantly subaverage intellectual functioning 2 and deficiencies in adaptive behavior
Written by the judges who cited it.
The opinion
CHIN, J.
I concur with the majority opinion, which I have signed. I write separately only to stress that although Penal Code section 1376 (section 1376) states no particular intelligence quotient (IQ) below which a person must score in order to be considered mentally retarded, standardized tests like IQ tests remain important. As the majority opinion explains (maj. opn., ante, at p. 47), section 1376’s standard is derived from Atkins v. Virginia (2002) 536 U.S. 304 [ 153 L.Ed.2d 335 , 122 S.Ct. 2242 ] (Atkins). The Atkins court said that the 70-75 IQ range “is typically considered the cutoff IQ score for the intellectual function prong of the mental retardation definition.” (Atkins, supra, at p. 309, fn. 5 .) Thus, a person whose IQ score is over 75 is very likely not mentally retarded, and in many, perhaps most, cases, a petitioner will not be entitled to relief absent a showing of an IQ at or below the 70-75 range.
Section 1376 defines mental retardation, in part, as including “significantly subaverage” intellectual functioning. (§ 1376, subd. (a).) The American Association on Mental Retardation (AAMR) states in its amicus curiae brief that “the term ‘significantly subaverage’ has been used by mental retardation professionals to describe the level of impairment found in individuals whose performance on standardized intelligence tests places them two standard deviations below the mean; that is, in the lowest two and a half or three percent of the population.” (Italics added.) This formulation is consistent with the Atkins court’s statement that between 1 and 3 percent of the population has an IQ between 70 and 75 or lower, the typical cutoff IQ for the intellectual function prong. (Atkins, supra, 536 U.S. at p. 309, fn. 5 .)
*53 Accordingly, to state a prima facie case regarding the intellectual function prong, petitioners must show that standardized intelligence tests, of which IQ tests are the most common, place them at least two standard deviations below the mean which, according to the AAMR, is roughly the lowest 2.5 to 3 percent of the population. They must also show that this intellectual deficiency manifested before the age of 18.
Kennard, J., concurred.
Petitioner’s petition for a rehearing was denied March 16, 2005. Brown, J., did not participate therein.