Volume 37, Issue 2 (2008)
Validity of the General Conceptual Ability Score From the Differential Ability Scales as a Function of Significant and Rare Interfactor Variability
Kasey M. Kotz, Marley W. Watkins, Paul A. McDermott
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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