As a high-stakes standardized test, IELTS is expected to have comparable forms of test papers so that test takers from different test administration on different dates receive comparable test scores. Therefore, this study examined the text difficulty and task characteristics of four parallel academic IELTS reading tests to reveal to what extent…

Research shows that test method can exert a significant impact on test takers' performance and thereby contaminate test scores. We argue that common test method can exert the same effect as common stimuli and violate the conditional independence assumption of item response theory models because, in general, subsets of items which have a shared…