English Department, Tabaran Institute of Higher Education
English Department, Islamic Azad University of Mashhad, Mashhad, Iran.
Reading comprehension in English, as one of the most central skills, has a vital role in the process of learning English as a Foreign/Second Language. The current study used the Mokken Scale Analysis (MSA), a probabilistic-nonparametric approach to item response theory (IRT), to determine the unidimensionality and scalability of a 20-item reading comprehension test administered on 300 EFL university students in the Iranian context. The results showed no major concerns in terms of item scalability. Monoton Homogeneity Model (MHM) fitted all the items of the test very well as measured by the scalability coefficients and restscore groups method. Considering the IIO, it was concluded that the ordering of items according to their mean is invariant across examinees although HT was small. Dimensionality analysis results using the AISP showed that the test is unidimensional providing evidence of the validity of the test in measuring a single ability dimension.