MODELING THE MIXTURE OF IRT AND PATTERN RESPONSES BY A MODIFIED HYBRID MODEL1

Abstract

This study demonstrates the utility of a HYBRID psychometric model, which incorporates both item response theoretic and latent class models, for detecting test speededness. The model isolates where in a sequence of test items examinee response patterns shift from ones providing reasonable estimates of ability to those best characterized by a random response pattern. The study applied the HYBRID model to three distinct data sets: (1) simulated data representing the performance of 3,000 examinees on a 70‐item test; (2) data from a statewide field test (n=5997 of a 40 item reading comprehension test with a fixed time limits; and (3) data from a study of urban university students (n=752) who took a similar 40‐item reading comprehension test under varying time limits. The HYBRID model successfully identified “switch points” in examinee's item response patterns in all three data sets. This paper discusses applications of the model used to detect speededness and to provide adjusted estimates of item parameters and examinee abilities.