Abstract
The difference (D) between a person's Verbal IQ (VIQ) and Performance IQ (PIQ) has for some time been considered clinically meaningful (Kaufman, 1976, 1979; Matarazzo, 1990, 1991; Matarazzo & Herman, 1985; Sattler, 1982; Wechsler, 1984). Particularly useful is information about the degree to which a difference (D) between scores is “abnormal” (i.e., deviant in a standardization group) as opposed to simply “reliable” (i.e., indicative of a true score difference) (Mittenberg, Thompson, & Schwartz, 1991; Silverstein, 1981; Payne & Jones, 1957). Payne and Jones (1957) proposed a formula to identify “abnormal” differences, which has been used extensively in the literature, and which has generally yielded good approximations to empirically determined “abnormal” differences (Silverstein, 1985; Matarazzo & Herman, 1985). However applications of this formula have not taken into account the dependence (demonstrated by Kaufman, 1976, 1979, and Matarazzo & Herman, 1985) of Ds on Full Scale IQs (FSIQs). This has led to overestimation of “abnormality” of Ds of high FSIQ children, and underestimation of “abnormality” of Ds of low FSIQ children. This article presents a formula for identification of abnormal WISC-R Ds, which overcomes these problems, by explicitly taking into account the dependence of Ds on FSIQs.
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