Mental retardation is a term for a pattern of persistently slow learning of basic motor and language skills ("milestones") during childhood, and a significantly below-normal global intellectual capacity as an adult. One common criterion for diagnosis of mental retardation is a tested intelligence quotient (IQ) of 70 or below and deficits in adaptive functioning.
People with mental retardation may be described as having developmental disabilities, global developmental delay, or learning difficulties.
Signs
There are many signs. For example, children with developmental disabilities may learn to sit up, to crawl, or to walk later than other children, or they may learn to talk later. Both adults and children with intellectual disabilities may also
* have trouble speaking
* find it hard to remember things
* have trouble understanding social rules
* have trouble discerning cause and effect
* have trouble solving problems
* have trouble thinking logically.
* persistence of infantile behaviour.
(ed.- Any of the above criterion sound familiar? Hmmm...)
In early childhood mild disability (IQ 60–70) may not be obvious, and may not be diagnosed until children begin school. Even when poor academic performance is recognized, it may take expert assessment to distinguish mild mental disability from learning disability or behavior problems. As they become adults, many people can live independently and may be considered by others in their community as "slow" rather than retarded.
Moderate disability (IQ 50–60) is nearly always obvious within the first years of life. These people will encounter difficulty in school, at home, and in the community. In many cases they will need to join special, usually separate, classes in school, but they can still progress to become functioning members of society. As adults they may live with their parents, in a supportive group home, or even semi-independently with significant supportive services to help them, for example, manage their finances.
Among people with intellectual disabilities, only about one in eight will score below 50 on IQ tests. A person with a more severe disability will need more intensive support and supervision his or her entire life.
The limitations of cognitive function will cause a child to learn and develop more slowly than a typical child. Children may take longer to learn to speak, walk, and take care of their personal needs such as dressing or eating. Learning will take them longer, require more repetition, and there may be some things they cannot learn. The extent of the limits of learning is a function of the severity of the disability.
Nevertheless, virtually every child is able to learn, develop, and grow to some extent.Diagnosis
According to the latest edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV),[5] there are three criteria before a person is considered to have a developmental disability: an IQ below 70, significant limitations in two or more areas of adaptive behavior (i.e., ability to function at age level in an ordinary environment), and evidence that the limitations became apparent in childhood.
It is formally diagnosed by professional assessment of intelligence and adaptive behavior.
IQ below 70
IQ tests were created as an attempt to measure a person's abilities in several areas, including language, numeracy and problem-solving. The average Caucasian score is 100. People with a score below 75 will often, but not always, have difficulties with daily living skills. Since factors other than mental ability (depression, anxiety, etc.) can yield low IQ scores, it is important for the evaluator to rule them out prior to concluding that measured IQ is "significantly below average".
The following ranges, based on the Wechsler Adult Intelligence Scale (WAIS), are in standard use today:
Class IQ
Profound mental retardation Below 20
Severe mental retardation 20–34
Moderate mental retardation 35–49
Mild mental retardation 50–69
Borderline mental retardation 70–79
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 the person's functioning in the community from someone who knows 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.