Mental Retardation and Developmental Disabilities

Diagnostic Criteria

The diagnostic criteria for MR are listed in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR) under the heading of “Disorders Usually First Diagnosed in Infancy, Childhood, and Adolescence” and can also be found in the American Association on Mental Retardation's (AAMR) Mental Retardation: Definition, Classification, and Systems of Supports, Tenth Edition. (Note: The AAMR has changed its name to the American Association on Intellectual and Developmental Disabilities.)

To warrant a diagnosis of MR, both of the following symptoms must be present in an individual prior to age 18: below average intellectual functioning and impairment in at least two areas of adaptive functioning.

Intellectual functioning is assessed using standardized instruments that measure an individual's intelligence quotient (IQ), such as the Wechsler Adult Intelligence Scale—Third Edition and the Stanford-Binet Intelligence Scales, Fifth Edition. Standardized IQ scores exist along a normal continuum, where a mean IQ score of 100 (standard deviation of 15) reflects an individual with average intelligence. To be considered for an MR diagnosis, individuals must have an IQ score approximately two standard deviations below the mean. This means that an IQ score of approximately 70 or below is needed to demonstrate significantly subpar intellectual functioning. Moreover, intellectual functioning is also coded to reflect the severity of impairment: mild (50–55 to approximately 70), moderate (35–40 to 50–55), severe (20–25 to 35–40), and profound (20–25 or below). Unspecified is the code given when there is a strong suspicion of MR, but actual IQ scores cannot be determined due to [Page 295]factors that interfere with IQ testing, such as uncooper-ativeness or extremely impaired functioning.

Adaptive functioning refers to activities needed to successfully navigate day-to-day demands of life. When individuals exhibit adaptive functioning deficits, they display consistent ineffectiveness in completing these daily activities. Levels of adaptive functioning are considered in light of the chronological age of an individual and are measured using standardized assessment instruments, such as the Vineland Adaptive Behavior Scales, Second Edition and the AAMR Adaptive Behavior Scale, Second Edition. The broad areas of adaptive functioning considered for an MR diagnosis include daily living skills, communication skills, and social and interpersonal skills. Daily living skills refer to a set of behaviors that center on self-care, household chores, work or academic involvement, and the ability to access community resources. Communication skills involve the ability to accurately understand others and express oneself. Social and interpersonal skills are the set of skills needed to successfully interact with others, cope with daily Stressors, and make use of free time. In addition to these three areas, deficits in fine and gross motor skills, such as toilet training and walking, may also be assessed in children.

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