Does Content Knowledge Affect TOEFL iBT™ Reading Performance? A Confirmatory Approach to Differential Item Functioning

ABSTRACT The TOEFL iBT™ has increased the length of the reading passages in the reading section compared to the passages on the TOEFL ® computer‐based test (CBT) to better approximate academic reading in North American universities, resulting in a reduced number of passages in the reading test. A concern arising from this change is whether the decrease in topic variety increases the likelihood that an examinee's familiarity with the particular content of a given passage will influence the examinee's reading performance. This study investigated differential item functioning and differential bundle functioning for six TOEFL iBT reading passages, three involving physical science and three involving cultural topics. The majority of items displayed little or no differential item functioning (DIF). When all of the items in a passage were examined, none of the passages showed differential functioning at the passage level. Hypotheses are provided for the DIF occurrences. Implications for fairness issues in test development are also discussed.