In dominant definitions of mental retardation, researchers have insisted on the diagnosis being restricted to conditions manifested during the developmental period. However, even in the 19th century, this was only one of several conceptual options, some of which did not exclude adult brain injury or dementia. Events in the 19th and early 20th…

Because persons with mental retardation cannot be executed for murder, the diagnosis becomes a life and death matter. The American Association on Mental Retardation (now the American Association on Intellectual and Developmental Disabilities) and other associations agree that IQ alone is an insufficient criterion and adaptive functioning also…