A More Restrictive Definition of "Mental Retardation" Excludes More People
In 1973, the American Association on Mental Deficiency changed its definition of mental retardation as:
Mental retardation refers to significantly sub-average general intellectual functioning existing concurrently with deficits in adaptive behavior, and manifested during the development period." (Grossman, 1977)
The AAMD also decided that the cut off for being labeled "mentally retarded" would be 70 on the IQ test. As Burton Blatt commented, millions of people were "cured" with this redefinition. Generally, this meant that only 2.25% of the population would be labeled instead of 16%.
The main reasons for dropping the borderline category were its racial implications (racial minority groups were over-represented in the borderline group) and a growing uneasiness about the effects of labeling. It also meant that fewer students were eligible for special education services. The new definition also extended the upper age limit of the developmental period to 18 years of age. That change was then reflected in the 1975 amendments to federal legislation.
This focus on adaptive behavior led to the development of scores of adaptive behavior scales that could measure the extent to which individuals' adaptive behaviors were deficient. These scales had their origins in the work of Goddard and Doll at The Vineland Training School in New Jersey. Goddard published his questionable work on The Kallikak Family. Doll developed the concept of adaptive behavior and the Vineland Social Maturity Scale in 1935. The scale was adopted by the U.S. military in 1941. It became the basis for the Vineland Adaptive Behavior Scale still in use today.