Abstract
Adaptive measurement of change (AMC) uses computerized adaptive testing (CAT) to measure and test the significance of intraindividual change on one or more latent traits. The extant AMC research has so far assumed that item parameter values are constant across testing occasions. Yet item parameters might change over time, a phenomenon termed item parameter drift (IPD). The current study examined AMC's performance in the context of IPD with unidimensional, dichotomous CATs across two testing occasions. A Monte Carlo simulation revealed that AMC false and true positive rates were primarily affected by changes in the difficulty parameter. False positive rates were related to the location of the drift items relative to the latent trait continuum, as the administration of more drift items spuriously increased the magnitude of estimated trait change. Moreover, true positive rates depended upon an interaction between the direction of difficulty parameter drift and the latent trait change trajectory. A follow-up simulation further showed that the number of items in the CAT with parameter drift impacted AMC false and true positive rates, with these relationships moderated by IPD characteristics and the latent trait change trajectory. It is recommended that test administrators confirm the absence of IPD prior to using AMC for measuring intraindividual change with educational and psychological tests.