If the purpose of an assessment is diagnosing examinees’ knowledge states to improve their learning, more fine-grained information than the overall level of their ability is necessary. Recent advances in diagnostic assessment triggered the development of cognitive diagnosis models (CDMs), such as the deterministic inputs, noisy “And” gate (DINA) model. Although CDMs for language assessments have been applied to reading or listening test data, a CDM may produce more practical results if the construct to measure has specific and well-defined skill attributes as in a grammar assessment. For this study, a grammar test consisting of 40 multiple-choice items was administered to 3,000 Korean learners of English as a foreign language. From the test items, a Q-matrix, which is an essential tool for CDMs, was constructed based on six grammar skills. As a result, skill profiles were obtained for all examinees. This diagnostic information can be used for tailored instruction. Issues with regard to applications of CDMs to language assessments are also discussed.

Differential item functioning (DIF) has been studied as a statistical method of finding item bias, and DIF studies have been conducted on tests of verbal abilities such as reading comprehension and vocabulary knowledge. Recently, researchers of language testing sought to understand the causes of DIF. The purpose of this study was to find possible sources of explaining DIF on an EFL vocabulary test, which can then benefit EFL learners and teachers as well. This study thus applied three DIF detection methods (the likelihood ratio test, SIBTEST, and the Mantel-Haenszel test), followed by a regression analysis using item categories and difficulties as predictors of explaining DIF. As a result, only the “Academic” category was statistically significant, positively contributing to DIF in favor of male examinees. Male examinees were better at academic lexical words than female learners of EFL at the same vocabulary knowledge level. This also means that female learners were relatively strong at nonacademic words in comparison to male EFL learners. This finding may lead to more effective curriculum of teaching English. The need for more evidence from replicated studies with better item categorization is also warranted.