Constraining item exposure in computerized adaptive testing with shadow tests

Item-exposure control in computerized adaptive testing is implemented by imposing item-ineligibility constraints on the assembly process of the shadow tests. The method resembles Sympson and Hetter's (1985) method of item-exposure control in that the decisions to impose the constraints are probabilistic. However, the method does not require time-consuming simulation studies to set values for control parameters prior to the operational use of the test. Instead, the probabilities of item ineligibility can be set "on the fly" using an adaptive procedure based on the actual item-exposure rates. An empirical study using an item pool from the Law School Admission Test (LSAT) showed that application of the method yielded perfect control of the item exposure rates and had negligible impact on the bias and MSE functions of the ability estimator.