The treatment of mentally retarded people has always reflected the changes in society. They have been officially referred to as idiots and as the feebleminded. The introduction of the IQ test was followed by a classification system that used such terms as moron (IQ of 51–70), imbecile (26–50), and idiot (0–25); later these terms were softened and classifications redefined somewhat to mild (IQ of 55–70), moderate (40–54), severe (25–39), and profound (0–24) retardation. The term mentally retarded itself, although still commonly used, has been replaced in some settings by the term developmentally disabled.
Mentally retarded people have been subjected to unnecessary institutionalization and, as a result of the eugenics movement, involuntary sterilization. The deinstitutionalization movement of the 1970s reflected a concern for the civil rights of mentally retarded. Very few of the mentally retarded are now institutionalized; most now live independently, with their families, or in group homes. The emphasis on education and self-sufficiency seen in the late 20th cent. mirrors a similar movement in the 1840s.