Validating Light Phenomena Conceptual Assessment Through The Lens of CTT and IRT Frameworks

Light phenomena conceptual assessment (LPCA) is a conceptual survey of light phenomena that has been recently established by the physics education research (PER) scholars. Studying the LPCA psychometric properties is always imperative to inform its measurement validity to potential LPCA users or beyond general educational researchers. Classical Test Theory (CTT) and Item Response Theory (IRT) are two popular statistical frameworks that can be utilized to explore the LPCA measurement validity. To our knowledge, no PER studies have been attempted to make a head-to-head comparison of those methods while validating the LPCA. This study was the first to delineate the LPCA measurement by statistically comparing the CTT and IRT based analysis. The LPCA dataset was drawn from physics students of eight secondary schools presented by Ndihokubwayo et al (2020). Our results accomplished the harmony between the CTT and IRT arguments to estimate the LPCA item performance and students' ability probed by the LPCA. They supported that the LPCA may be used as inventory for evaluating conceptual understanding of light phenomena from low to high students' ability range even some flagged LPCA items were exist based on CTT and IRT arguments. Special considerations for further refinement related to the discriminating power for some problematic LPCA items are discussed.