Diagnostic Value Resulting from the IRT Modeling of IGAP Reading Data: Using A Graded Response Model To Retrieve and Utilize More Information.

The strengths of item-response theory (IRT) are used to examine the degree of information individual test items provide, as well as to investigate how the individual item types contribute to the overall measurement accuracy of the Illinois Goal Assessment Program (IGAP) reading test. Using the graded-response model of Samejima (1969), the amount of information each subtest (narrative and expository) provides about the underlying latent ability is studied. Where an item type provides the most information along this ability scale, and how the different item formats (e.g., number of correct inferences) differ in terms of ability to discriminate between levels of reading proficiency are also studied. Data sets of 4,837, 4,840, and 5,011 randomly selected examinees were obtained for grades 3, 6, and 8, respectively. While the expository subtest is generally more informative than the narrative subtest across the three grade levels for low to moderate theta values, the difference does not appear to be substantial. The graded response model appears to be a promising tool that allows examination of the information from each subtest. Fourteen figures illustrate the findings. (Contains 10 references. (SLD)