Test Dimensionality and Conditional Independence of Undergraduate Physics Test Items of National Open University of Nigeria: Perspective from Latent Traits Model (Ltm) Package of R Language

Abstract

Physics test items developed by the National Open University of Nigeria (NOUN) to measure test-takers' proficiency in Elementary Mechanics, Heat, and Properties of Matter (PHY101) are intrinsically multidimensional. However, we observed the current method used by the University to score test-takers proficiency in the course is premised on Classical Test Theory, which has been criticised in the literature for its limitations, and a measurement model for unidimensional tests. Consequently, using an inappropriate model to model test-takers responses to items would adversely affect their true proficiency in the course. Therefore, this study assessed the dimensionality and conditional independence of physics test items of NOUN using the ltm package in the R language. A non-experimental design of survey research type was adopted. Test-takers responses to the 35 PHY 101 multiple-choice items across NOUN study centres in the 36 States of Nigeria were retrieved from the Directorate of Examination of Assessment (DEA) and used for the study, with empirical reliability of 0.80. Nine hundred seventy-eight test-takers responses were captured and analysed with modified parallel analysis test and Yen Q3 statistics implemented in ltm package of R language software, version 4.0.2. Findings remarked that NOUN physics items had more than one predominant dimension to account for the observed performance of test-takers in the course. Also, residual correlations of ten item pairs severely violated the conditional independence benchmark of 0.20. We conclude that PHY 101 of NOUN is intrinsically multidimensional. Test-takers responses to the test items are due to their locations on multiple latent variables. We recommend that a psychometric unit be established within the DEA of the University to check the appropriateness of the test items developed by the faculty lecturers.