Confirmatory factor analysis of the Iowa tests of basic skills

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Abstract
Confirmatory factor analysis was used to explore the internal structural validity of the Iowa Tests of Basic Skills (ITBS) using three samples: (a) the third-grade standardization sample, (b) a fourth-grade sample reported by Klein (1981), and (c) a new sample of third graders. Results showed that a four-factor structure provided a better representation of the relations among the 11 subtests than Klein's one-factor model, a two-factor model, or the three-factor model described in the ITBS manual. The four-factor model was refined using the new sample and was cross-validated using the other two samples. A hierarchical model with a single, second-order general achievement factor was also found to fit the data well. Decomposition of subtest variance into common, specific, and error components indicated that little specific variance is associated with several ITBS subtests, raising the question of whether interpretation of individual subtests is warranted.

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