Mental Retardation

The most widely used definition of mental retardation (MR) in the United States is:

This definition is from the American Association of Mental Retardation (AAMR), which has had [Page 318]responsibility for defining mental retardation since 1921 (Luckasson & colleagues, 2002).

Intellectual functioning is generally assessed by means of a standardized intelligence test, resulting in an intelligence quotient (IQ). The IQ must be below 70 or 75 for a person to be considered mentally retarded. Adaptive behavior or skills include conceptual (e.g., receptive and expressive language), social (e.g., interpersonal skills), and practical (e.g., personal self-help skills). Adaptive skills can be assessed by adaptive behavior scales, observations, and anecdotal records. When applying this definition, AAMR states that professionals must consider the following five assumptions:

• 1.
  Limitations in present functioning must be considered within the context of community environments typical of the individual's age, peers, and culture.
• 2.
  Valid assessments must consider cultural and linguistic diversity as well as differences in communication, sensory, motor, and behavioral factors.
• 3.
  Limitations often coexist with strengths within an individual.
• 4.
  Descriptions of limitations help develop a profile of needed supports.
• 5.
  Life functioning of a person with mental retardation will generally improve with appropriate personalized supports over a sustained period.

Once a person has been identified as an individual with MR, AAMR advocates determining the level of supports (intermittent, limited, extensive, pervasive) needed to provide the person with the ability to function as independently as possible within the community. Intermittent supports are episodic or short-term (as needed), and may be either low or high intensity. The key factor to limited support is consistency despite less time, fewer staff, and/or lower costs. Extensive supports occur regularly and are not timelimited. Pervasive supports are both constant and high intensity, involve more staff, are the most intrusive, and occur in the most environments. Thompson and colleagues (2004) developed the Supports Intensity Scale to assist professionals in determining the level of support needs for an individual in seven areas of competence: home living, community living, lifelong learning, employment, health and safety, social interaction, and protection and advocacy (e.g., protecting self from exploitation, exercising legal responsibilities). Additional information is also gathered on exceptional medical (e.g., respiratory care, skin care) and behavioral needs (e.g., self-directed destructiveness, sexual). The composite score from the scale is used to determine the need for supports and the level of intensity.

Another frequently used definition for MR is provided by the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) (1994), which provides thorough diagnostic criteria for medical and health care professionals in the United States. The DSM-IV version is based on the 1992 AAMR definition, but it retains the levels of severity (mild, moderate, severe, and profound) used in the 1972 AAMR definition. Approximately 85% of individuals classified as mentally retarded fall within the mild range (IQ from 50–55 to approximately 70), 10% fall within the moderate range (IQ 35–40 to 50–55), 3% to 4% fall within the severe range (IQ 20–25 to 35–40), and 1% to 2% fall within the profound range (IQ below 20–25). Deficits must also occur in at least two of the following adaptive functioning areas: communication, health, leisure time, safety, school, self-care, social, taking care of a home, and work. Again, age of onset must occur before age 18 years.

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