The role of language background in the validation of a computer-adaptive test

The use of item response theory (IRT) analysis has greatly facilitated the development of computer adaptive tests, in which the adaptiveness is based on measures of item difficulty resulting from the performance of trial test-takers. However, studies into the acquisition of second language (L2) grammar by learners with different first languages (L1s) indicate that the learners' L1 strongly influences their acquisition of grammar in the L2. Thus, it would be expected that grammar test items would present different levers of difficulty to test-takers from different language backgrounds. When a computer-adaptive grammar test is to be used with test-takers from a range of language backgrounds, it is, therefore, questionable whether set item difficulty measures can validly be used for all types of test-taker.