Adaptive Behavior Assessments

Intellectual Disabilities and Adaptive Behavior Skills

A deficit in adaptive behavior skills has not always been a part of assessment for intellectual disabilities. When the American Psychiatric Association first published the Diagnostic and Statistical Manual of Mental Disorders (DSM) in 1952, the classification category of mental deficiency was introduced to account for cases that were primarily a defect of intelligence present at birth with no known organic brain disease or known prenatal cause for the deficits. Cases were to include only individuals with familial or idiopathic (unknown origin) mental deficiencies, and severity was to be determined by IQ scores in the following three ranges: mild (an IQ of approximately 70–85), moderate (IQ 50–70), and severe (IQs below 50). Although IQ scores were necessary to determine the range and expectations, the DSM noted the importance of considering other factors.

When the second edition of DSM (DSM-II) was first published in 1968, the term mental retardation (MR) replaced mentally deficient. The DSM-II better aligned with what was then called the American Association on Mental Retardation (now the American Association on Intellectual and Developmental Disabilities) and supported five ranges of severity (borderline, mild, moderate, severe, and profound), with the borderline range for IQ scores in the 68–85 range. It listed clinical codes for 9 subcategories for the disorder, based on the circumstances of origin (e.g., following infection and intoxication; following trauma or physical agent).

In 1980, the DSM-III placed MR in a new section titled “Disorders Usually First Evident in Infancy, Childhood or Adolescence.” The three main criteria for a diagnosis of MR remained consistent with the previous version (i.e., impaired IQ, impaired adaptive behaviors, and onset during the developmental period); however, these criteria were further refined at this time. Subnormal intelligence was now set two standard deviations below the mean (IQ of 70), instead of one standard deviation (IQ of 85) with the addition of a five-point interval to be considered (IQ 65–75) to account for the standard error of measure. Onset during the developmental period was defined as occurring below 18 years of age. Impairments in [Page 41]adaptive functioning were required; however, the DSM noted that the then-current measures were not considered valid to be used in isolation to make this decision and recommended that clinical judgment should evaluate adaptive functioning in individuals relative to similar aged peers.

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