A confirmatory approach to differential item functioning on an ESL reading assessment

In this article, I describe a practical application of the Roussos and Stout (1996) multidimensional analysis framework for interpreting group performance differences on an ESL reading proficiency test. Although a variety of statistical methods have been developed for flagging test items that function differentially for equal ability examinees from different ethnic, linguistic, or gender groups, the standard differential item functioning (DIF) detection and review procedures have not been very useful in explaining why DIF occurs in the flagged items (Standards for Educational and Psychological Testing 1999). To address this problem, Douglas, Roussos and Stout (1996) developed a confirmatory approach to DIF, which is used to test DIF hypotheses that are generated from theory and substantive item analyses. In the study described in this paper, DIF and differential bundle functioning (DBF) analyses were conducted to determine whether groups of reading test items, classified according to a bottom-up, top-down reading strategy framework, functioned differentially for equal ability Arabic and Mandarin ESL learners. SIBTEST (Stout and Roussos, 1999) analyses revealed significant systematic group differences in two of the bottom-up and two of the top-down reading strategy categories. These results demonstrate the utility of employing a theoretical framework for interpreting group differences on a reading test.