A Confirmatory Factor Analytic Study Examining the Dimensionality of Educational Achievement Tests

Along with the increasing popularity of item response theory (IRT) in testing practices, it is important to check a fundamental assumption of most of the popular IRT models, which is unidimensionality. Nevertheless, it is hard for educational and psychological tests to be strictly unidimensional. The tests studied in this paper are from a standardized high-stake testing program. They feature potential multidimensionality by presenting various item types and item sets. Confirmatory factor analyses with one-factor and bifactor models, and based on both linear structural equation modeling approach and nonlinear IRT approach were conducted. The competing models were compared and the implications of the bifactor model for checking essential unidimensionality were discussed. Examining Test Dimensionality 3