Advances in test adaptivity to improve measurement in testlet-based computerized adaptive test

A set of items that includes a common stimulus such as a reading passage, picture, graphic, or scenario is called testlet and has been used frequently in educational assessments. However, due to the presence of a common stimulus in testlet, it is possible that the local independence assumption may be violated. The violation of local item independence due to testlets may also affect the performance of computerized adaptive testing (CAT). This study examines how different factors impact the performance of testlet-based CAT in a simulation study. The manipulated conditions included adaptation level (testlets vs. items), testlet/item selection approaches, the magnitude of testlet dependencies, and test length, testlet size, and number of testlets. One of the important findings of the study is that adaptation not only between testlets but also within testlets improved the performance of CAT, resulting in less biased latent trait estimation and a smaller standard error of measurement.