Abstract
This study used Item Response Theory approach to assess Differential Item Functioning (DIF) and detect item bias in Mathematics Achievement Test (MAT). The MAT was administered to 1,751 SS2 students in public secondary schools in Cross River State. Instrumentation research design was used to develop and validate a 50-item instrument. Data were analysed using the maximum likelihood estimation technique of BILOG-MG V3 software. The result of the study revealed that 6% of the total items exhibited differential item functioning between the male and female students. Based on the analysis, the study observed that there was sex bias on some of the test items in the MAT. DIF analysis attempt at eliminating irrelevant factors and sources of bias from any kind for a test to yield valid results is among the best methods of recent. As such, test developers and policymakers are recommended to take into serious consideration and exercise care in fair test practice by dedicating effort to more unbiased test development and decision making. Examination bodies should adopt the Item Response Theory in educational testing and test developers should therefore be mindful of the test items that can cause bias in response pattern between male and female students or any sub-group of consideration.
 Keywords: Assessment, Differential Item Functioning, Validity, Reliability, Test Fairness, Item Bias, Item Response Theory.
Highlights
Fairness in assessment of students’ achievement tests in mathematics in our secondary schools is very fundamental as mathematics is the basis for studying other subjects especially in science related courses
Fairness is an essential quality of a test; its equitable treatment of all examinees during the testing process, absence of measurement bias, equitable access to the constructs being measured, and justifiable validity of test score interpretation for the intended purpose Every assessment provides formative and summative data on students’ learning and achievements through which specific acquired competencies could be acquired by efficient teaching and learning process
If we find males with the same mathematics ability as females had a greater probability of responding correctly to an item than females, the item would be identified as functioning differently across gender. This means the achievement test item is measuring mathematics ability, and measuring a second unrelated factor known as sex
Summary
Fairness in assessment of students’ achievement tests in mathematics in our secondary schools is very fundamental as mathematics is the basis for studying other subjects especially in science related courses. Testing for differential item functioning is an investigation to know whether performance on any test item differs for certain groups of examinees that is, male and female students. If we find males with the same mathematics ability as females had a greater probability of responding correctly to an item than females, the item would be identified as functioning differently across gender. This means the achievement test item is measuring mathematics ability, and measuring a second unrelated factor known as sex.
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