combining data from intellectual and adaptive functioning in order to provide a complete profile of an individual’s capabilities, and (e) clarify ways of better differentiating mental retardation from other conditions with which it shares signs and symptoms. The committee has also been asked to provide suggestions for research or evaluation that could clarify unaddressed or incompletely answered issues. This report answers these questions and makes specific recommendations as well.


Although no single definition of mental retardation is universally accepted in all its details, intellectual deficits are central to all such definitions. The consensus of the major professional associations and health-related organizations is that mental retardation involves deficits in intellectual functioning and adaptive behavior and has its onset during the developmental period. Their definitions differ from each other on a number of critical specifics, including the nature and measurement of the deficits in adaptive behavior and the age of onset.

SSA’s definition of mental retardation includes the criteria used by these authoritative sources. However, it diverges from the standard diagnostic nomenclature in some ways, including the nature and assessment of deficits in adaptive behavior, its basis for determining subaverage intellectual functioning, and the age of onset. In addition, the SSA definition goes beyond the criteria used by these other organizations in identifying individuals as having mental retardation if they have both deficits in intellectual functioning and comorbid medical or psychiatric disorders—a circumstance addressed by no other definition of mental retardation.

It is important to note that the differences between the SSA definition of mental retardation and those of the major professional and health-related organizations derive from the purpose for which it is used. The SSA definition is used not for diagnostic purposes, but rather for purposes of program eligibility. The SSA definition fulfills its purpose of identifying individuals with cognitive limitations who

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