A mental retardation diagnosis occurs when a patient meets specific criteria, as set forth by manuals like the Diagnostic and Statistical Manuals® (DSM®) or the International Classification of Diseases, which tend to be similar in nature. Both manuals call for a measure of IQ that falls well below normal, and an onset of the disorder before the age of 18. In addition, the person must show impairment in several key areas.
Proving a mental retardation diagnosis may begin with intelligence quotient (IQ) testing. Typically an IQ of 70 is considered the cutoff point, but this isn’t completely accurate. Some mental retardation advocacy organizations feel an IQ of 70 plus or minus five is more appropriate. Therefore, an IQ score as high as 75 might be considered indicative of this disorder.
There are distinctions between profound, severe, moderate, and mild mental retardation, which are based on intelligence quotient measures. In profound mental retardation, IQ falls below 20-25, while those with a severe mental retardation diagnosis have an IQ ranging between 20-25 and 40. People with moderate forms of this disorder could have IQs between 35-55, and those with a mild disorder typically have IQ levels from 50-70, plus or minus five. There is some overlap in each category, with slight differences between the DSM® and the International Classification of Diseases.
People with mental retardation may show measurable, functional impairment in several areas of life. These include the ability to provide self-care, social and interpersonal skills, success in academic settings, and degree of independence. Other vital functional areas are communication skills, leisure activities, and self-safety. Physical health and the ability to take advantage of resources in the community round out the list. There must be marked impairment in at least two areas to make a mental retardation diagnosis.
For example, a person might be impaired at school, and not be able to appropriately interact with peers and neighbors due to impaired social skills. When this is combined with an IQ below 75, and an identifiable age of onset before 18, it is enough to justify a mental retardation diagnosis. Many permutations of impairments are possible. Generally, number of areas in which someone is impaired rises with decreasing IQ levels.
Low IQ scores aren’t enough to result in a mental retardation diagnosis. It is possible for a person with low testing scores to have no functional impairment or to behave in culturally expected ways that may appear impaired in a new culture. Clinicians need to give significant thought to whether a person’s behavior or “impairment” arises from cultural upbringing or is truly representative of mental retardation. Also, if the person is being diagnosed after turning 18, the diagnostician must establish that the condition was present before that age.