NCJ Number
85947
Date Published
1981
Length
135 pages
Annotation
This report explains the development of a latent trait model for responses on test items scored in two or more ordered categories.
Abstract
The 'partial credit' model is a member of the family of latent trait models which share the property of parameter separability, and so permit 'specifically objective' comparisons of persons and items. The model can be viewed as an extension of Andrich's rating scale model to situations in which ordered response alternatives are free to vary in number and structure from item to item. The difference between the parameters in this model and the 'category boundaries' in Samejima's graded response model is demonstrated. An unconditional maximum likelihood procedure for estimating the model parameters is developed, and applications of the model to a screening test and an attitude questionnaire are described. Tables and charts are given. A 38-item bibliography is provided. (Author abstract modified)