Impact of Item Bias on NECO 2017 Mathematics Exam Reliability in Nigeria

This study examines the impact of item bias on the reliability of examinee scores in the 2017 NECO Mathematics Senior Secondary Certificate Examination (SSCE) in Nigeria using modern psychometric techniques. A stratified random sample of 256,039 SSS III students were analyzed across gender, school location, and school type. Responses were calibrated in R, and three hypotheses were tested at the 0.05 significance level. Results show that item bias significantly affects score reliability, with empirical reliability coefficients of 0.99 (gender), 0.99 (school location), and 0.98 (school type), compared to an overall test reliability of 0.90. These findings suggest that factors unrelated to ability, such as demographic characteristics, can distort performance outcomes. To improve fairness and validity, the study recommends robust norming procedures, representative sampling, and standardized item development. Addressing item bias is essential for equitable assessment and public trust in national examinations.