Abstract

This study analysed item fit and differential functioning of senior secondary school mathematics test in Rivers State using the Rasch model. Guided by two research questions and null hypotheses, the study adopted an instrumentation research design. The population consisted of 199,602 Rivers State public senior secondary school students for the 2025/2026 academic year, from which a sample of 480 participants was drawn using a multi-stage sampling technique. A researcher- developed instrument titled “Mathematics Performance Test for Senior Secondary School Two Students”, was used for data collection. The instrument was validated by two senior secondary school mathematics teachers and a Measurement and Evaluation expert at Rivers State University. The reliability coefficient was calculated using Kuder–Richardson Formula 20, yielding α = 0.73. Data were analysed using the Rasch model with the eRm package in R. Results showed that all the items of the senior secondary school mathematics test demonstrated acceptable fit to the Rasch measurement model, and the test items do not demonstrate differential item functioning by gender. It was recommended that mathematics educators collaborate with measurement specialists to utilise the Rasch model throughout item construction to detect and evaluate possible item misfit and guarantee that all items exhibit adequate fit. Also, schools should always review their mathematics test items for differential item functioning by gender to be satisfied that the test does not introduce gender-related bias before administering to students.