To meet the criteria for the diagnosis of Mental Retardation, three areas must be considered.
- Onset must occur before 18 years of age. In addition, the person must have
- Below average general intellectual functioning. General intellectual functioning is defined by the intelligence quotient (IQ) obtained by assessment with one or more of the standardized, individually administered intelligence tests. The choice of testing instrument and interpretation of results should take into account factors that may affect test performance, such as sociocultural background, native language and associated communication, and motor and sensory handicaps. Specialized tests may be used to measure other aspects of development.
Intellectual impairment is categorized by four degrees of severity. These classifications suggest the types of interventions that would be appropriate and offer clues as to long-term outcome.
- Mild retardation: Mild retardation: IQ level 50-55 to approximately 70 (85% of people with mental retardation are in this category)
- Moderate retardation: IQ level 35-40 to 50-55 (10% of people with mental retardation)
- Severe retardation: IQ level 20-25 to 35-40 (3 - 4% of people with mental retardation)
- Profound retardation: IQ level below 20 or 25 (1 - 2% of people with mental retardation)
- Significant limitations in adaptive functioning in at least two of the following skill areas: communication, self-care, home living, social/interpersonal skills, use of community resources, self-direction, functional academic skills, work, leisure, health and safety.