In educational context, Differential Item Functioning (Dif) and Differential Bundle Functioning (Dbf) are usually used in assessing item bias. In present study, it is demonstrated how results of Dif and Dbf analyses can help in better understanding the reasons behind one country’s underachievement in international assessments. In Timss 2011 mathematics assessment, Croatian fourth graders achieved a mean result that was below the international average, while Slovenian and Serbian students achieved mean results that were above the international average. The results of Dif and Dbf analyses indicate that large portion of items exhibiting differences in favour of Slovenian and Serbian students are related to topics that are not taught in Croatian schools during first four grades. The described methodology can be used in investigating other countries’ (under)achievement in international assessments.
Keywords: International differences, differential item functioning, differential bundle functioning, mathematics, Timss