Examining the Nature of Item Bias on Students’ Performance in National Examinations Council (NECO) Mathematics Senior School Certificate Dichotomously Scored Items in Nigeria

This study examined the nature of item bias on students’ performance in 2017 National Examinations Council (NECO) mathematics senior school certificate dichotomously scored items in Nigeria. The study adopted an ex-post-facto research design. A sample of 256,039 candidates was randomly selected from the population of 1,034,629 students who took the test. Instrument for data collection was 'Student Results' (SR). Data collected were analysed using the R language environment and an independent t-test. Results showed that the 2017 NECO Mathematics test was essentially unidimensional (-0.28 (<.20), ASSI = -0.31 (< 0.25) and RATIO = -0.31 (< 0.36). Results also showed that the nature of bias statistically encountered was a mean difference in scores bias, indicating that 86% (52 items), 79.1% (34 items), and 96% (56 items) were biased against male students, urban and public-school students, respectively. It was concluded that item bias is a notable factor that affected the validity of the NECO 2017 Mathematics test and conclusions drawn from the scores in Nigeria. Hence, it was recommended that before tests are administered for public use, examination bodies should make a careful review of tests through dimensionality assessment at the developmental stage to eliminate any perspectives that could cause test inequity among examinees.