According to the American Association on Mental Deficiency (AAMD), intellectual disability is characterized by:

Significantly sub-average general intellectual functioning and deficits in adaptive behavior.

The American Association on Mental Deficiency (AAMD) views intellectual disability as “significantly sub-average general intellectual functioning existing concurrently with deficits in adaptive behaviour and manifested during the developmental period”. This definition points to three basic features. First, in order to be judged as intellectually disabled, a person must show significantly sub-average intellectual functioning. Persons having IQs below 70 are judged to have sub-average intelligence. The second relates to deficits in adaptive behaviour. Adaptive behaviour refers to a person’s capacity to be independent and deal effectively with one’s environment. The third feature is that the deficits must be observed during the developmental period, that is between 0 and 18 years of age.