This tutorial addresses possible sources of confusion in interpreting trait scores from the bifactor model. The bifactor model may be used when subscores are desired, either for formative feedback on an achievement test or for theoretically different constructs on a psychological test. The bifactor model is often chosen because it requires fewer…

The purpose of this study was to explore the degree of grain size of the attributes and the sample sizes that can support accurate parameter recovery with the General Diagnostic Model (GDM) for a large-scale international assessment. In this resampling study, bootstrap samples were obtained from the 2003 Grade 8 TIMSS in Mathematics at varying…

Studies of international mathematics achievement such as the Trends in Mathematics and Science Study (TIMSS) have employed classical test theory and item response theory to rank individuals within a latent ability continuum. Although these approaches have provided insights into comparisons between countries, they have yet to examine how specific…