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There are three steps in the diagnosis of mental retardation:
- Standardized testing
- Intelligence testing
- Adaptive skills testing
- Determining strengths and weaknesses across 4 dimensions:
- Intellectual and adaptive behavior skills
- Psychological/emotional considerations
- Physical/health/etiological considerations
- Environmental considerations
- Determining supports needed and the level of intensity:
- Intermittent
- Limited
- Extensive
- Pervasive
According to the latest edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), three criteria must be met for a diagnosis of mental retardation: an IQ below 70, significant limitations in two or more areas of adaptive behavior (as measured by an adaptive behavior rating scale, i.e. communication, self-help skills, interpersonal skills, and more), and evidence that the limitations became apparent before the age of 18. It is formally diagnosed by professional assessment of intelligence and adaptive behavior.
The following ranges, based on Standard Scores of intelligence tests, reflect the categories of the American Association of Mental Retardation, the Diagnostic and Statistical Manual of Mental Disorders-IV-TR, and the International Classification of Diseases-10:
Since the diagnosis is not based only on IQ scores, but must also take into consideration a person's adaptive functioning, the diagnosis is not made rigidly. It encompasses intellectual scores, adaptive functioning scores from an adaptive behavior rating scale based on descriptions of known abilities provided by someone familiar with the person, and also the observations of the assessment examiner who is able to find out directly from the person what he or she can understand, communicate, and the like.
Significant limitations in two or more areas of adaptive behavior
Adaptive behavior, or adaptive functioning, refers to the skills needed to live independently (or at the minimally acceptable level for age). To assess adaptive behavior, professionals compare the functional abilities of a child to those of other children of similar age. To measure adaptive behavior, professionals use structured interviews, with which they systematically elicit information about persons' functioning in the community from people who know them well. There are many adaptive behavior scales, and accurate assessment of the quality of someone's adaptive behavior requires clinical judgment as well. Certain skills are important to adaptive behavior, such as:
- daily living skills, such as getting dressed, using the bathroom and feeding oneself;
- communication skills, such as understanding what is said and being able to answer
- social skills with peers, family members, spouses, adults and others.
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