The Effect of Deleting Content-Related Items on IRT Ability Estimates

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Abstract
In this study, the process a school might use to build a "customized test" from an "on shelf' standardized achievement test was followed, as closely as possible. The main purpose was to assess the effects of using "customized test" results rather than full test results in estimating examinee ability levels. To this end, ability parameters were estimated for groups of students on the Quantitative Thinking subtest of a standardized achievement test battery as well as on customized versions of the test. It was found that the ability estimates from the full-length tests and those from the customized tests at times differed substantially.