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Abstract
Surveillance and epidemiologic research on intellectual disability often do not incorporate adaptive functioning (AF) data. Exclusion of AF data leads to overestimation of the prevalence of intellectual disability, the extent of which is not known. In this study, the authors evaluated the effect of incorporating AF data on overall intellectual disability prevalence according to sociodemographic, economic, and severity characteristics. Between 2002 and 2006, the Metropolitan Atlanta Developmental Disabilities Surveillance Program identified 1,595 8-year-old children who met the study's intellectual disability surveillance-case definition of IQ ≤ 70. AF scores were not available for 9.2% of the case children, specifically those with mild intellectual disability and low socioeconomic backgrounds. Prevalence estimates showed few substantive changes when incorporating AF data. The authors conclude that use of IQ data alone appears to be appropriate for measuring population intellectual disability prevalence.
DOI: 10.1352/1944-7558-116.5.360
Since its inception, the American Association on Intellectual and Developmental Disability (AAIDD; formerly the American Association on Mental Retardation [AAMR]) has been the primary organization involved in defining intellectual disability. The current definition of intellectual disability represents an ongoing emphasis to move away from the use of impaired cognition alone to a definition that also incorporates the functioning of an individual in their environment. AAIDD currently defines intellectual disability as a disability characterized by significant limitations both in intellectual functioning (reasoning, learning, and problem solving) and in adaptive behavior (conceptual, social, and practical adaptive skills) originating before the age of 18 years (AAMR, 2002).
Population-based prevalence estimates for intellectual disability have shown substantial variation, ranging from = to 42 per 1,000 children in developing countries, with the majority within a closer range of 10 to 15 per 1,000 children (Van Naarden Braun & Yeargin-Allsopp, 2009). These differences are influenced by numerous factors, including the definitions used, methods of ascertainment, availability of standardized intelligence and adaptive behavior test results, reliability of diagnosis, and the characteristics of populations studied. Adaptive functioning (AF) data have been widely accepted as a necessary component of the intellectual disability definition for clinical diagnosis and service provision yet have not been commonly included in epidemiological studies. Studies conducted in the late 1970s and early 1980s found that incorporating AF criteria into measurement of intellectual disability prevalence resulted in a decreased prevalence of...