Uses of Rasch modeling in counseling psychology research.

Inferences made from summary indices of psychometric scales must be reliable and valid to advance scientific knowledge in counseling psychology. This article illustrates traditional and innovative uses of the Rasch model in the development and validation of small- and large-scale psychological instruments. Discussion of traditional uses of the Rasch model included reliability and validity of scale scores, whereas discussion of innovative uses included (a) determining the optimal number of response categories for Likert-type items and (b) obtaining a measure of response style for each person. Both mathematical and conceptual explanations are provided, and counseling psychology data are used to illustrate examples.