Computerized adaptive testing using the nearest-neighbors criterion

Item selection procedures designed for computerized adaptive testing need to accurately estimate every taker's trait level (theta) and, at the same time, effectively use all items in a bank. Empirical studies showed that classical item selection procedures based on maximizing Fisher or other related information yielded highly varied item exposure rates; with these procedures, some items were frequently used whereas others were rarely selected. In the literature, methods have been proposed for controlling exposure rates; they tend to affect the accuracy in theta estimates, however. A modified version of the maximum Fisher information (MFI) criterion, coined the nearest-neighbors (NN) criterion, is proposed in this study. The NN procedure improves to a moderate extent the undesirable item exposure rates associated with the MFI criterion and keeps sufficient precision in theta estimates. The NN criterion will be compared with a few other existing methods in an empirical study using the mean squared errors in theta estimates and plots of item exposure rates associated with different theta distributions.