Relationships between Cognitive Diagnosis, CTT, and IRT Indices: An Empirical Investigation

Cognitive diagnosis models (CDMs) continue to generate interest among researchers and practitioners because they can provide diagnostic information relevant to classroom instruction and student learning. However, its modeling component has outpaced its complementary component-test construction. Thus, most applications of cognitive diagnosis modeling involve retrofitting of CDMs to assessments constructed using classical test theory (CTT) or item response theory (IRT). This study explores the relationship between item statistics used in the CTT, IRT, and CDM frameworks using such an assessment, specifically a large-scale mathematics assessment. Furthermore, by highlighting differences between tests with varying levels of diagnosticity using a measure of item discrimination from a CDM approach, this study empirically uncovers some important CTT and IRT item characteristics. These results can be used to formulate practical guidelines in using IRT- or CTT-constructed assessments for cognitive diagnosis purposes.