Gender-related impact and differential item functioning in a test of numerical ability

Gender-related impact and differential item functioning in a test of numerical ability. Standardized tests reflect differences between groups, and we should distinguish whether they are real or a product of the measuring instrument itself. In the last few decades psychometric research has approached this problem with the growing development of the studies of the differential item functioning for subjects or groups with the same degree of ability. This study examines the possible existence of real differences (impact) according to gender in a test of numerical ability and the possible differential item functioning (DIF), with two different procedures. The first is based on item response theory and the second on confirmatory factor analysis. Results suggest a careful review of the content of several items of the test. An examination of the convergence of results obtained with the different procedures supports the use of iterative purification mechanisms when working with confirmatory factor analytic techniques and the use of multiple convergent evidences in taking decisions in empirical studies.