The committee recommends continuation of the criterion of presumptive eligibility for persons with IQs below 60.

The use of part scores, most often from the Wechsler measures, introduces an important consideration in the clinical use of intelligence measures for disability determination. Current scientific conceptions of intelligence focus primarily on fluid and crystallized abilities, with recognition that working or comprehensive memory is also important to overall intellectual functioning. Many intelligence tests are based on these distinctions. The Wechsler measures are also moving in this direction, with a focus on factor scores that are analogous to crystallized intelligence (e.g., verbal comprehension index), fluid intelligence (e.g., perceptual organization index), and working/comprehensive memory (e.g., working memory index). Consequently, the committee has recommended continued use of part scores in eligibility determination, but is advocating use of part scores that are consistent with current scientific thinking.

ADAPTIVE BEHAVIOR AND ITS ASSESSMENT

Deficits in adaptive behavior, together with deficits in intelligence, are also central to current definitions of mental retardation. SSA and the major professional organizations disagree on the nature and degree

   

Therefore, a score of 70 or below on either of these part scores from any standardized, individually administered intelligence test that reports such scores should be deemed sufficient to meet the listings for low general intellectual functioning regardless of the level of the composite score, providing that the part scores have adequate psychometric properties (e.g., high reliability, low standard error of measurement). Dr. Widaman notes that, without any clear justification, SSA currently accepts either a composite IQ score from any standardized, individually administered intelligence test or a verbal or performance IQ score, any one of which can be 70 or below. SSA does not stipulate that the composite IQ must be below a certain score for a part score to be used. Dr. Widaman’s position provides a rationale for current SSA use of part scores, but it (a) aligns the acceptable part scores with the constructs of Gc and Gf used in contemporary theories of mental abilities and (b) argues that usable part scores for Gc and Gf should not be limited to those derived from any particular test instrument.



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