As defined in ICD-10, mental retardation is a condition of arrested or incomplete cognitive developmen, which is particularly characterized by impairment manifested during the developmental period, of skills which contribute to a person’s overall level of intelligence (cognitive, language, motor, and social abilities). Degrees of mental retardation are conventionally estimated by standardized intelligence tests. These can be supplemented by scales assessing social adaptation in a given environment. Intellectual abilities and social adaptation may change over time, and, however poor, may improve as a result of training and rehabilitation.

There are four degrees of mental retardation:

– mild mental retardation: approximate IQ range of 50 to 69 (in adults, mental age from 9 to under 12 years). Likely to result in some learning difficulties in school. Many adults will be able to work and maintain good social relationships and contribute to society.

– moderate mental retardation: approximate IQ range of 35 to 49 (in adults, mental age from 6 to under 9 years). Most can learn to develop some degree of independence in self-care and acquire adequate communication and academic skills. Adults will need varying degrees of support to live and work in the community.

– severe mental retardation: approximate IQ range of 20 to 34 (in adults, mental age from 3 to under 6 years). Likely to result in a continued need for support.

– profound mental retardation: IQ under 20 (in adults, mental age below 3 years). Results in severe limitation in self-care, communication and mobility.