PURPOSE: Assessment in different languages should measure the same construct. However, item characteristics, such as item flaws and content, may favor one test-taker group over another. This is known as item bias. Although some studies have focused on item bias, little is known about item bias and its association with items characteristics. Therefore, this study investigated the association between item characteristics and bias.
METHODS: The University of Groningen offers both an international and a national bachelor's program in medicine. Students in both programs take the same progress test, but the international progress test is literally translated into English from the Dutch version. Differential item functioning was calculated to analyze item bias in four subsequent progress tests. Items were also classified by their categories, number of alternatives, item flaw, item length, and whether it was a case-based question.
RESULTS: The proportion of items with bias ranged from 34% to 36% for the various tests. The number of items and the size of their bias was very similar in both programmes. We have identified that the more complex items with more alternatives favored the national students, whereas shorter items and fewer alternatives favored the international students.
CONCLUSION: Although nearly 35% of all items contain bias, the distribution and the size of the bias were similar for both groups. The findings of this paper may be used to improve the writing process of the items, by avoiding some characteristics that may benefit one group whilst being a disadvantage for others.