Characterizing Sampling Variability for Item Response Theory Scale Scores in a Fixed-Parameter Calibrated Projection Design.

A common practice of linking uses estimated item parameters to calculate projected scores. This procedure fails to account for the carry-over sampling variability. Neglecting sampling variability could consequently lead to understated uncertainty for Item Response Theory (IRT) scale scores. To address the issue, we apply a Multiple Imputation (MI) approach to adjust the Posterior Standard Deviations of IRT scale scores. The MI procedure involves drawing multiple sets of plausible values from an approximate sampling distribution of the estimated item parameters. When two scales to be linked were previously calibrated, item parameters can be fixed at their original published scales, and the latent variable means and covariances of the two scales can then be estimated conditional on the fixed item parameters. The conditional estimation procedure is a special case of Restricted Recalibration (RR), in which the asymptotic sampling distribution of estimated parameters follows from the general theory of pseudo Maximum Likelihood (ML) estimation. We evaluate the combination of RR and MI by a simulation study to examine the impact of carry-over sampling variability under various simulation conditions. We also illustrate how to apply the proposed method to real data by revisiting Thissen et al. (2015).