fied with commonly used instruments. Differences in content, standardization, and floor and ceiling effects on broadly used measures of adaptive behavior, as well as different conceptualizations of the nature of adaptive behavior, all contribute to this difficulty. Current estimates suggest that anywhere from 1 to 3 percent of people living in the United States will receive a diagnosis of mental retardation. These varying prevalence estimates reflect (1) differences in the way that mental retardation is defined, interpreted, and measured; (2) differences in the ways in which students are identified in urban and rural education systems; and (3) whether individuals or their families from varying cultural, racial, and ethnic backgrounds choose to apply for services. In addition, definitions of mental retardation vary, with SSA, the major professional organizations, and the World Health Organization all providing different definitions of the condition.

SSA provides income support and medical benefits to many individuals with mental retardation. Benefits are provided to adults unable to perform substantial gainful activity (i.e., work) because of mental retardation through the Disability Insurance (DI) program and the Supplemental Security Income (SSI) program. SSI benefits are provided as well to the families of children and adolescents who evidence “marked and severe” restrictions in functioning because of mental retardation. The determination decisions are made through state disability determination services, with payments coming from the federal agency and, in some jurisdictions, supplemented by state resources.


Specifically, the committee has been asked to (a) examine the adequacy of the SSA definition of mental retardation, (b) comment on the current procedures for assessing intellectual capabilities and indicate how best to make that assessment consistent with current science and professional practice, (c) discuss the issue of adaptive behavior and its assessment consistent with current science and widespread professional practice, (d) provide advice on the most appropriate ways of

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