Inferences made from summary indices of psychometric scales must be re
liable and valid to advance scientific knowledge in counseling psychol
ogy. This article illustrates traditional and innovative uses of the R
asch 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 disc
ussion of innovative uses included (a) determining the optimal number
of response categories for Likert-type items and (b) obtaining a measu
re of response style for each person. Both mathematical and conceptual
explanations are provided, and counseling psychology data are used to
illustrate examples.