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Society regards normal intelligence as an ability to function easily in everyday life and in academic subjects. Intelligence quotient (IQ) tests can be useful tools to represent intellectual ability through a number. Those people who do not have an intellectual disability have an IQ of more than 70, where 100 is the average of the population. Degrees of intellectual disability also apply, and a person with a mild intellectual disability typically has an IQ of 55 to 70, although this is an arbitrary range that may vary by health authority. Usually, to fall into the intellectually disabled portion of the population, a person also must need support to deal with daily life.
IQ tests measure the ability of a person to use information to complete tasks and figure out how to answer complex questions without rote learning. This roughly translates to the intellectual ability of the person being tested, and is correlated with both academic achievement and ability to handle everyday life. As this particular test measures individuals against an entire population, the average score of the population is always 100.
A score of 70 or less indicates that a person does not have a level of intellectual skills that typically allow him or her to navigate school and life without extra support. This score therefore acts as one of the criteria for inclusion into the group of people with intellectual disabilities. Some people, however, with a score of 70 or less, are able to lead a normal life, and these people generally are not regarded by health authorities as intellectually disabled.
Most people with an IQ score of 70 or less are intellectually disabled. Mental retardation or cognitive disability are terms that are interchangeable with intellectual disability. Degrees of severity of the disability exist, and health authorities generally call these mild, moderate, severe and profound.
If someone has an IQ of 50 to 70, and problems handling daily life, then they fall into a widely accepted definition of a mild intellectual disability. 35 to 50 is moderate and 20 to 35 is severe. A result of less than 20 usually means that the person is profoundly disabled.
Children with a mild intellectual disability are often able to go to a regular school if the school has extra support systems in place to help them learn along with the kids who fall into the normal range. Although the kids may be able to function happily and learn relatively successfully, they may be a few years behind the other children in the class with regard to the things they can understand and remember. Other possible problems a child with intellectual disability may have include a short attention span, poor memory and a lack of social skills.
Adults with a mild intellectual disability may be able to live alone, get married and earn their own living, if they have family support or help from other sources like health authorities. Often, people who have this disability also have physical problems, like cerebral palsy or seizures. Genetic conditions like Down Syndrome are a common cause of intellectual disabilities, but problems in the womb, such as a pregnant woman ingesting high levels of alcohol, can also adversely affect intellectual development. Historically, infections like rubella often caused intellectual damage to babies in the womb, but vaccinations mean these causes are less prevalent than before.