An Investigation into Differential Item Functioning of Tests Conducted by the Two Major Examination Bodies in Nigeria


Differential Item Functioning (DIF) is a condition where a test item functions differently for examinees from one group to another. This study deals with an investigation into the differential item functioning of test conducted by the two major Examination bodies in Nigeria viz; the West African Examination Council and the National Examination Council. The major objective was to find out if the test items from the two examination bodies will function differently in terms of location (urban and rural) of the examinees. The award of ordinary level certificates is solely the responsibility of these two examination bodies in Nigeria. These bodies use the Classical Test Theory (CTT) principles in analyzing their test items. It is necessary to determine whether the test items function differently in terms of location using the Item Response Theory (IRT) principles of analysis.Item analysis is a crucial part of the test development process. The two prevailing methods are the CTT and IRT. The CTT has been popular because of its ease of use and adaptability in analyzing all kinds of tests. Two research questions were posed while one hypothesis was tested. The WAEC and NECO examination questions for the year 2002 were administered to senior secondary three students from the three education zones of Benue State. The Maximum Likelihood Estimation technique of the BILOG MG Computer programme was used to answer the research questions while t-test was used to test the hypothesis. The sample for the study comprised one thousand eight hundred (1800) Senior Secondary year three students from three education zone of Benue State, Nigeria. The study lasted for one year. The result showed that there was no significant difference in the differential functioning of items from the two examination bodies. However, it was recommended that the IRT analysis should be adopted by all examination bodies in Nigeria because of its qualities.