A Note on Evaluation of Polytomous Item Locations With the Rating Scale Model and Testing Its Fit

Abstract

A procedure is outlined for point and interval estimation of location parameters associated with polytomous items, or raters assessing studied subjects or cases, which follow the rating scale model. The method is developed within the framework of latent variable modeling, and is readily applied in empirical research using popular software. The approach permits testing the goodness of fit of this widely used model, which represents a rather parsimonious item response theory model as a means of description and explanation of an analyzed data set. The procedure allows examination of important aspects of the functioning of measuring instruments with polytomous ordinal items, which may also constitute person assessments furnished by teachers, counselors, judges, raters, or clinicians. The described method is illustrated using an empirical example.