Four item response theory (IRT) models were compared using data from tests where multiple items were grouped into testlets focused on a common stimulus. In the bi-factor model each item was treated as a function of a primary trait plus a nuisance trait due to the testlet; in the testlet-effects model the slopes in the direction of the testlet…

Using the notion of parallel items this paper presents a family of new criteria for cluster analysis. (Author)

A method for the construction of scales which combines the rational (or intuitive) approach with an empirical (item analysis) approach is presented. A step-by-step procedure is provided. (Author/JKS)

National Assessment of Educational Progress reading data were scaled using a unidimensional item response theory model. Bock's full-information factor analysis and Rosenbaum's test of unidimensionality were applied. Conclusions about unidimensionality for balanced incomplete block spiralled data were the same as for complete data. (Author/GDC)

Causes of differential item difficulty for blind students taking the braille edition of the Scholastic Aptitude Test's mathematical section were studied. Data for 261 blind students were compared with data for 8,015 non-handicapped students. Results show an association between selected item categories and differential item functioning. (TJH)

This study investigates whether a linear factor analytic method commonly used to evaluate violation of the item response theory (IRT) unidimensionality assumption is sensitive to measurable curricular differences within a school district and to examine the possibility of differential item performance for groups of students receiving different…