Effect of Item Bundling on the Assessment of Test Dimensionality. Laboratory of Psychometric and Evaluative Research Report No. 328.

The primary purpose of this study was to assess the effect of item bundling on multidimensional data. A second purpose was to compare three methods for assessing dimensionality. Eight multidimensional data sets consisting of 100 items and 1,000 examinees were simulated varying in terms of dimensionality, inter-dimensional correlation, and number of items loading on each dimension. Analyses were also performed on two samples of examinees from the November 1996 administration of the Uniform Certified Public Accountant examination. The items from both data sets were grouped into bundles that varied in size and content. Principal components factor analysis, maximum likelihood factor analysis, and multidimensional scaling were used to analyze the item bundles as well as the items themselves. Results suggest that item bundling tends to obscure multidimensionality, but analyses on the items themselves overestimate dimensionality. Multidimensional scaling also appeared better able to recover the underlying dimensionality of the data than the other two techniques. (Contains 13 tables and 17 references.) (Author/SLD)