Considerations for the Diagnosis of Intellectual Disability

The diagnosis of intellectual disability (ID) requires adaptive dysfunction as well as "significantly subaverage intellectual functioning, i.e., an IQ of approximately 70 or below on an individually administered IQ test" (DSM-IV). Factor structures in the WISC-IV permit discrepancies between verbal and nonverbal estimates of intelligence, as well as providing for an overall IQ composite. Formal diagnostic criteria do not specify if one, two, or all of these scores should be in the impaired range to satisfy the criteria of "subaverage intellectual functioning." The proposed study will seek to determine which of these scores should be in the impaired range to satisfy the criteria for a diagnosis of ID by comparing the cognitive and adaptive functioning of children who have low/impaired scores in verbal intelligence only, nonverbal intelligence only, or both.