In a 1973 article in American Psychologist, Heber presented a revised definition of mental retardation for the American Association on Mental Deficiency (AAMD, later AAMR). He explicitly proposed that mental retardation be defined as significantly subaverage general intellectual functioning, with an IQ "approximately 70 or below" rather than the previous standard of 85 or below, in combination with deficits in adaptive behavior, with onset before the age of 18. The article discusses psychometric and conceptual reasons for changing the cutoff point, but does not attribute the change to racial test-score distributions or to the proportion of African Americans scoring below any specific IQ threshold.

Describing historical definitions, the report notes: "Subaverage intellectual functioning was defined as an IQ of 85 or less, with the developmental period extending only up to age 16." It then explains that, over time, the IQ threshold and other criteria were revised toward a more restrictive definition centered around approximately 2 standard deviations below the mean (about IQ 70) in combination with adaptive behavior deficits. The discussion links the change to evolving professional standards and psychometric reasoning, not to the racial composition of low-IQ groups.

“One standard deviation below the mean on an intelligence test was delineated as the point at which intellectual functioning should be considered subnormal (Heber, 1961). This specification meant that on an IQ test with a mean of 100 and a standard deviation of 15, any score below 85 would be diagnostic of mental retardation… If the total population was tested and classified on this basis, almost 16% would be diagnosed as having mental retardation.” “In 1973 an AAMR committee again revised the definition. The committee constructed this revision with criticism of the 1961 definition in mind. It specified that significantly subaverage general intellectual functioning was to be determined by a score of at least two standard deviations below the mean on an intelligence test (Grossman, 1973). This meant that the cutoff point for mental retardation was essentially moved downward from 85 to 70. This change lowered the percentage of the population that might be identified as having mental retardation from 16% to approximately 2.25%.” The author then notes: “This revision meant that fewer people would be labeled retarded because of language differences, socioeconomic factors, or minority status.”

The AAMR 1992 manual, which traces the evolution of the association's definitions, states that by 1973 the AAMD adopted an IQ cutoff of approximately 70 and below as indicative of "significantly subaverage intellectual functioning." The manual describes the change from earlier higher cutoffs as reflecting a shift to a statistical criterion of roughly two standard deviations below the mean and a greater emphasis on adaptive behavior. It does not cite racial test‑score distributions or the proportion of African Americans below any IQ level as the reason for the 1973 change.

A National Research Council/IOM report on mental retardation notes that historically, IQ cutoffs in classification systems have shifted over time. It states that earlier definitions sometimes used cutoffs around 85, but that professional organizations moved to a criterion of about 70 (two standard deviations below the mean) in the 1970s to better align with psychometric theory and service needs. The discussion is framed in terms of statistical norms, diagnostic validity, and service eligibility; it does not describe the 1973 AAMD change as being driven by the distribution of IQ scores among African Americans or by the fact that any racial group had more than half of its members below 85.

A historical review of definitions of mental retardation in American Psychologist describes the evolution from broad, often socially based classifications to ones grounded in psychometrics and adaptive behavior. The review notes that earlier standards sometimes used an IQ of 85 as a rough upper boundary, but that by the early 1970s the field had converged on a more restrictive IQ criterion around 70 coupled with adaptive behavior deficits. The article identifies concerns about over‑diagnosis, improved test norming, and conceptual clarity as reasons for the shift, and it does not attribute the 1973 change to concerns about African American IQ distributions.

“In 1973, the American Association on Mental Deficiency changed its definition of mental retardation as: ‘Mental retardation refers to significantly sub-average general intellectual functioning existing concurrently with deficits in adaptive behavior, and manifested during the development period.’ (Grossman, 1977). The AAMD also decided that the cut off for being labeled ‘mentally retarded’ would be 70 on the IQ test.” The same page explains: “Generally, this meant that only 2.25% of the population would be labeled instead of 16%. The main reasons for dropping the borderline category were its racial implications (racial minority groups were over-represented in the borderline group) and a growing uneasiness about the effects of labeling.”

The excerpt notes that by the end of the 1950s “the AAMR announced full support for expanding the criteria for the identification of individuals with MR beyond the sole criterion of the IQ score to include: an IQ score of less than 85; impairment in adaptive behavior; and onset prior to 18 years of age.” Later it states that “changes in civil rights legislation and concerns about the misplacement of African American children in classes for the educable mentally retarded in special education led to changes in the criteria for MR, lowering the IQ to 70 from 85 (Grossman, 1973).” It adds that this drop “meant a shift that would require an individual to score 2 SDs below the mean on an IQ test to be within the MR Range. Approximately 2% of the population would obtain an IQ of 70 or less.”

The APA explains the modern standard: "Traditionally, cognitive or intellectual functioning has been measured through the intelligence quotient (IQ) tests, with an IQ of less than 70 recommended for a clinical diagnosis of Intellectual Disability." It notes that "A full-scale IQ score of around 70 to 75 indicates a significant limitation in intellectual functioning" and that diagnosis also depends on adaptive skills. The page describes the psychometric rationale and clinical practice surrounding the <70 threshold, but does not attribute its historical adoption to concerns about African American test scores.

Encyclopaedia Britannica’s entry on intellectual disability explains that in modern diagnostic practice, intellectual disability is typically defined as an IQ of about 70 or below, together with significant limitations in adaptive behavior, emerging during the developmental period. The article notes that older terminology such as "mental retardation" and earlier classification systems once relied more heavily on IQ alone and sometimes used higher IQ thresholds, but that these were revised in the 20th century as understanding of intelligence testing improved. The entry does not mention racial distributions of IQ or any claim that changes in IQ cutoffs were made because more than half of African Americans scored below 85.

This education brief explains: “Prior to 1973, the recommended IQ cut-off score for mental retardation was 85. In 1973, that was revised downwards to approximately 70, where it remains today. This is roughly the lowest scoring 2% of the population.” It further notes that “The low IQ score alone is insufficient for a diagnosis of mental retardation” and that diagnosis requires an IQ of approximately 70 or below, deficits in adaptive behavior, and onset before age 18.

The APA newsletter describes diagnostic criteria: "Intellectual disability is characterized by significant limitations in both intellectual functioning (an IQ score of approximately 70 or below) and in adaptive behavior." It notes that these criteria derive from long-standing professional definitions by organizations such as the AAMR/AAIDD and are grounded in the convention of two standard deviations below the mean. The article does not suggest that the IQ cutoff was adjusted in response to racial score distributions.

The historical overview reiterates that the AAMR definition was revised in 1973: “In 1973, in response to criticisms of the 1961 definition, AAMD (later AAMR) adopted a new definition that required both ‘significantly subaverage general intellectual functioning,’ defined as an IQ of approximately 70 or below (i.e., 2 SDs below the mean), and concurrent deficits in adaptive behavior with onset before age 18.” The chapter notes that criticisms included overidentification and misuse in educational placements, especially for minority children, but does not present a claim that the cutoff was changed specifically because ‘more than half of African Americans scored below 85.’

An APA disability resources article summarizing the history of intellectual disability states that during the 20th century, diagnostic criteria evolved from broad social categories to ones focusing on measurable intellectual functioning and adaptive behavior. It notes that IQ cutoffs around 70 became standard as the field sought to identify individuals with significant impairments, and that terms and criteria from older manuals, such as broader ranges including those with IQs in the 70s and 80s, were phased out. The article does not mention racial IQ distributions or suggest that changes in cutoff points were made because of the proportion of African Americans below any particular IQ score.

Human Rights Watch summarizes the historical changes: “The threshold I.Q. level for a diagnosis of mental retardation has been progressively lowered over the years, in part because of awareness of the damaging social prejudice suffered by those labeled ‘retarded.’ In 1959, the American Association on Mental Deficiency set 85 as the I.Q. below which a person was considered to be retarded.” It continues: “In 1992, the renamed American Association on Mental Retardation lowered the mental retardation ‘ceiling’ to an I.Q. of 70-75 … With the upper ceiling on mental retardation reduced from an I.Q. of 85 to an I.Q. of 70, far fewer Americans are today diagnosed as ‘mentally retarded’ than before.”

The APA PsycNet record for Grossman’s “A Manual on Terminology and Classification in Mental Retardation” (Washington, DC: American Association on Mental Deficiency, 1973) describes it as the official AAMD manual revising definitions and classifications of mental retardation. Secondary summaries of this manual report that it defined “significantly subaverage general intellectual functioning” as performance 2 standard deviations below the mean (approximately IQ 70) with concurrent deficits in adaptive behavior and onset before age 18. Publicly available bibliographic descriptions do not mention a rationale based on ‘more than half of African Americans scoring below 85’; instead, later historical analyses cite concerns about overidentification of minority children and misuse of IQ tests as reasons for the change.

A historical analysis of the 1973 AAMD definition (accessed via JSTOR) explains that one impetus for the change from a 1 SD (IQ <85) to a 2 SD (IQ ≈70) cutoff was growing criticism that the earlier definition led to widespread misclassification, including disproportionate placement of minority and low‑income children in classes for the ‘educable mentally retarded.’ The article frames the revision as a response to professional, legal, and civil-rights pressures about the overuse and misuse of the mental retardation label, rather than presenting a specific quantitative claim that ‘more than half of African Americans scored below 85.’

In Larry P. v. Riles, federal courts examined evidence that standardized IQ tests used by California schools resulted in a disproportionate number of Black children being placed in classes for the educable mentally retarded. The litigation record notes that a high percentage of African American children scored in ranges that, under then‑current classification systems, made them eligible for EMR placement. The case illustrates the broader context of concern over racial bias and disproportionate classification that surrounded and followed the 1973 AAMR/AAMD definitional changes, but the court materials do not state that the 1973 IQ cutoff change was specifically because ‘more than half of African Americans scored below 85.’

This textbook chapter notes the historical shift: “In 1973, the IQ cutoff was again changed back to 2 standard deviations below the mean; however, the benchmark of a measurable impairment in adaptive behavior was retained.” Earlier in the chapter, it explains that an IQ of 85 is one standard deviation below the mean and that definitions of intellectual disability evolved to emphasize both IQ and adaptive behavior, situating the 1973 change in the broader professional effort to align diagnostic criteria with statistical norms.

The history section of the intellectual disability article notes that professional organizations and diagnostic manuals gradually narrowed the IQ range used to define intellectual disability, settling around two standard deviations below the mean (IQ of about 70) by the 1970s. It mentions that prior definitions sometimes included individuals with IQs up to the mid‑80s, but these were later excluded as the field emphasized adaptive functioning and statistical norms. The article does not state that any change was made specifically because more than half of African Americans scored below 85 on IQ tests, nor does it link diagnostic thresholds to racial score distributions.

The article on race and intelligence summarizes psychometric research showing that, in many 20th‑century U.S. studies, African American test takers scored on average about one standard deviation (roughly 15 IQ points) below white test takers, with a mean often reported around 85. It also notes that these distributions imply that a relatively larger share of African Americans than whites score below conventional cutoffs such as 70 or 85. However, the article presents these findings as descriptive of test-score disparities and does not state that the American Association on Mental Retardation changed its IQ cutoff in 1973 because more than half of African Americans scored below 85.

An article published in the journal Mental Retardation (Vol. 22, No. 1, AAMR) describes the then-current identification practices of U.S. states following the adoption of the AAMR definitions. While the full text focuses on how states applied criteria such as IQ cutoffs and adaptive behavior, it reflects that the association’s recommended IQ threshold for mental retardation was around 70, consistent with two standard deviations below the mean. The article does not describe the change as motivated by the proportion of African Americans below any particular IQ score, but rather in terms of professional diagnostic standards.

Under a standard IQ test with mean 100 and standard deviation 15, a cutoff at 85 (one standard deviation below the mean) classifies about 16% of the general population as below that threshold, while a cutoff at 70 (two standard deviations below the mean) classifies about 2–2.5%. This matches historical descriptions that an IQ ceiling of 85 would include approximately 16% of the population and that lowering it to 70 reduced the labeled group to roughly 2–2.5%. These figures apply to the total tested population and do not themselves specify racial breakdowns or motives for professional policy changes.

A social media post summarizing the history states: “In 1973, the AAMR changed the IQ threshold for mental retardation from below 85 to below 70 to reduce overdiagnosis, particularly among minorities.” This explanation attributes the change broadly to concerns about overdiagnosis of minority students, but it does not provide evidence or citation for a specific claim that the threshold was changed because more than half of African Americans scored below 85.