Academic journal article School Psychology Review

Validity of the General Conceptual Ability Score from the Differential Ability Scales as a Function of Significant and Rare Interfactor Variability

Academic journal article School Psychology Review

Validity of the General Conceptual Ability Score from the Differential Ability Scales as a Function of Significant and Rare Interfactor Variability

Article excerpt

Abstract. Some researchers have argued that discrepant broad index scores invalidate IQs, but others have questioned the fundamental logic of that argument. To resolve this debate, the present study used a nationally representative sample of children (N=1,200) who were matched individually for IQ. Children with significantly uneven broad index score profiles and those with even broad index score profiles had equivalent reading and math skills. Discrepant broad index scores found in only 15%, 10%, 5%, and 1% of the population, respectively, also failed to differentially predict academic achievement. In addition, significantly higher Verbal broad index scores were not differentially predictive of reading achievement, nor were significantly higher Nonverbal/Spatial broad index scores differentially predictive of math achievement. It was concluded that the global ability score is the most parsimonious predictor of academic achievement, despite the presence of significant and rare variability among broad index scores.

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Every year, millions of assessments that include a measure of intelligence are conducted (Sattler, 2001). Although only a portion of the competencies included in human intelligence is assessed, the results of these ability measures provide the best available long-range predictors of student achievement, school adjustment, level of vocational attainment, and job performance (Gottfredson, 1997, 2004; Kubiszyn et al., 2000; Sattler, 2001; Schmidt & Hunter, 2004). Therefore, the measurement of intelligence can aid in the prediction of a range of important educational and occupational criteria (Braden, 1997). Consequently, examiners ought to render accurate and relevant interpretations of intelligence measures.

The omnibus or global Intelligence Quotient (IQ) is commonly used as a predictor of academic achievement. Many clinicians, however, attempt to extract additional information from lower level subcomponents of the intelligence test, such as broad index scores and subtest scores (Donders, 1996; Kaufman, 1994; Kaufman & Lichtenberger, 2000). These lower level scores are then organized to form profiles of broad index or subtest scores. Although analysis of subtest scores has been historically popular, subtests should not be used for the prediction of achievement (Glutting, McDermott, Konold, Snelbaker, & Watkins, 1998; McDermott & Glutting, 1997; Watkins & Glutting, 2000). Even advocates of subtest analysis admit that this method should not be used for more than the examination of individual differences within a particular client (Kaufman, 1994; Sattler, 2001).

Unlike subtest analysis, broad index score analysis has increased in popularity (Prifitera, Saklofske, & Weiss, 2005). Some psychologists have argued that interfactor discrepancies invalidate the IQ, especially for the prediction of achievement (Hale & Fiorello, 2001; Hale, Fiorello, Kavanagh, Hoeppner, & Gaither, 2001; Lichtenberger, Kaufman, & Lai, 2002). This position has gained wide currency in clinical practice (Pfeiffer, Reddy, Kletzel, Schmelzer, & Boyer, 2000), and devaluation of the IQ in the presence of an uneven broad index score profile is often suggested in the professional literature (Drummond, 2004; Kaufman, 1994; Kaufman & Lichtenberger, 2002; Lezak, 1995; Sattler & Dumont, 2004; Weiss, Saklofske, & Prifitera, 2005). However, some researchers have challenged this interpretation and suggested that the IQ is the best predictor of academic outcomes despite broad index score variability (Glutting, Youngstrom, Ward, Ward, & Hale, 1997; Kline, Snyder, Guilmette, & Castellanos, 1993; Oh, Glutting, Watkins, Youngstrom, & McDermott, 2004; Watkins & Kush, 1994; Youngstrom, Kogos, & Glutting, 1999). In fact, Glutting, Watkins, Konold, and McDermott (2006) asserted that when observed ability scores are used to predict achievement, only the IQ, an indicator of general intelligence, is needed. …

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