Including Empirical Prior Information in the Reliable Change Index.

The reliable change index (RCI; Jacobson & Truax, 1991) is commonly used to assess whether individuals have changed across two measurement occasions, and has seen many augmentations and improvements since its initial conception. In this study, we extend an item response theory version of the RCI presented by Jabrayilov et al. (2016) by including empirical priors in the associated RCI computations whenever group-level differences are quantifiable given post-test response information. Based on a reanalysis and extension of a previous simulation study, we demonstrate that although a small amount of bias is added to the estimates of the latent trait differences when no true change is present, including empirical prior information will generally improve the Type I behavior of the model-based RCI. Consequently, when non-zero changes in the latent trait are present the bias and sampling variability are show to be more favorable than competing estimators, subsequently leading to an increase in power to detect non-zero changes.