observational in format, had burgeoned, including checklists pertaining to vocational behaviors (Walls & Werner, 1977). Measures developed in the 1960s have typically been updated in subsequent editions with enhanced psychometric characteristics and scoring (e.g., Sparrow & Cicchetti, 1985).

Over the past 25 years there has also been further refinement of the parameters and structure of tests of adaptive behavior and social competence. This refinement was based on large samples of research participants and data from service registries (McGrew & Bruininks, 1990; Siperstein & Leffert, 1997; Widaman et al., 1987, 1993). Novel frameworks for conceptualization of adaptive behavior have been proposed (American Association on Mental Retardation, 1992), and conventional frameworks have been endorsed for application in differential diagnosis and classification practices (Jacobson & Mulick, 1996). Finally, the difficulties and complexities of differentiating mild mental retardation from its absence or from other disabling conditions (e.g., Gresham et al., 1995; MacMillan, Gresham, et al., 1996; MacMillan, Siperstein, & Gresham, 1996) have remained an enduring concern in both professional practice and policy formulation.

Differing Conceptualizations

In Chapter 1 we summarized the history of definitions of mental retardation and discussed their relevance to the Social Security Administration’s definition. At first glance, current definitions seem to be quite similar; however, there are subtle differences in the conceptualization of adaptive behavior that may affect the outcomes of diagnostic decisions for individuals with mental retardation, particularly those in the mild range.

In the recent Manual of Diagnosis and Professional Practice in Mental Retardation (Jacobson & Mulick, 1996), Division 33 of the American Psychological Association put forth a definition of mental retardation that emphasizes significant limitations in intellectual functioning and adaptive behavior. The definition also views adaptive behavior as

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