Improving the Matching for DIF Analysis by Conditioning on Both Test Score and an Educational Background Variable

Abstract

When tests are designed to measure dimensionally complex material, DIF analysis with matching based on the total test score may be inappropriate. Previous research has demonstrated that matching can be improved by using multiple internal or both internal and external measures to more completely account for the latent ability space. The present article extends this line of research by examining the potential to improve matching by conditioning simultaneously on test score and a categorical variable representing the educational background of the examinees. The responses of male and female examinees from a test of medical competence were analyzed using a logistic regression procedure. Results show a substantial reduction in the number of items identified as displaying significant DIF when conditioning is based on total test score and a variable representing educational background as opposed to total test score only.