Differential performance on OECD PISA tests: Evaluating item functioning methods using mathematics assessments

Differential Item Functioning (DIF) occurs when item parameters change over different sub-groups of subjects. DIF can be manifest and/or latent. Previous studies have shown that DIF can be due to the multidimensionality of the latent trait. In this study, we checked the unidimensionality of the OECD-PISA mathematics achievement test administered in 2018 via the analysis of both manifest and latent DIF. Data analysis showed a few items showing statistically significant and large manifest DIF. Nonetheless, the combined use of both the overall fit statistics and the analysis of the latent DIF confirmed that the unidimensionality of the OECD-PISA achievement test analysed in the current study.