As item response models gain increased popularity in large-scale educational and measurement testing situations, many studies have been conducted on the development and applications of unidimensional and multidimensional models. Recently, attention has been paid to IRT-based models with an overall ability dimension underlying several ability…

The research project presented in this article was set in the Swedish school context and carried out on a set of compulsory national tests for English, Swedish, and mathematics used at the end of compulsory school. The aims were: (a) to gain a deeper knowledge of the internal structure of the tests and (b) to separate individual performance from…