ASSESSMENT OF ITEM BIAS IN THE EQUATED SCORES OF THE 2021 NECO SENIOR SECONDARY CERTIFICATE EXAMINATION (SSCE) FOR AGRICULTURAL SCIENCE IN NORTH CENTRAL NIGERIA

Abstract

This study investigated the comparability of scores from the 2021 NECO Senior Secondary Certificate Examination (SSCE) for Agricultural Science in North Central Nigeria, specifically focusing on item bias and score equating between internal and external test forms. The research highlights the potential issues in using different test forms, which can introduce variations in difficulty levels, leading to unfair comparisons and impacting decisions such as university admissions and scholarships. A non-equivalent anchor test (NEAT) design was used to compare two test forms with common items, adjusting for differences in difficulty. The population consisted of 97,413 Senior Secondary students in the North Central region, with 89,680 internal and 7,733 external candidates. A sample of 2,682 students was selected using a multi-stage sampling method. Data were collected through a self-structured proforma, “NECO Agricultural Science OMR Score Retrieval Proforma,” which included information on test items, student scores, and gender. The data were analysed using Item Response Theory (IRT), with the mean equating method and Exploratory Structural Equation Modeling (ESEM) to address the research questions. The study found significant differences in the mean ability estimates when scaled through mean equating, suggesting that raw and equated scores were not identical. Additionally, 17 items in the internal test and 10 items in the external test exhibited bias based on school type, potentially due to variations in teaching methods, teacher experience, and available resources. The study recommended among others: refining equating methods, ensuring test item fairness, and improving teaching resources to address biases and improve score comparability.