EXAMINING THE RELATIONSHIP BETWEEN THE RASCH AND 2-PL MODELS OF IRT IN SELECTING ITEMS IN A CONSTRUCTED TEST FOR CURRICULUM DEVELOPMENT

Abstract

Test developments are critical in the measurement of learning and education attainments. Its precision and accuracy is a major task in an academic setting in Nigeria and beyond. The scales employed for achievement tests are often based on classical test theory (CTT) approach with a drawback of the variability of results in different samples of the same population or from the same pool of items in some Africa countries like Nigeria. This work explores the method of the Rasch model and the 2-PL model of Item Response Theory (IRT) to examine the relationship between the models used on a constructed Mathematics Aptitude Test (MAT) items. A 120 items instrument with a reliability value of 0.86 was developed by the researcher. Mean Square (MNSQ) and ZSTD of fitness of Winsteps and Two-Parameter Model (2-PL) of Bilog-Mg3 were used to investigate how well the Mathematics fit the Models. Eventually, thirty-three (33) items whose parameters are known scaled through the Rasch model and were confirmed to measure the same construct (uni-dimensionality) while 13 items are significant but do not fit into the 2-PL model at p< 0.05. Rasch shows that only 33 items fit into the model while the 2-PL model shows that 107 items fit into its model. This shows that a great disparity occurs between Rasch and 2-PL model. These items are banked for curriculum development purposes. This paper concludes that the Rasch model is preferred to the 2-PL model and therefore recommends its usage in curriculum development in Nigerian schools and Examination bodies in Africa and beyond.