Exploring dimensionality of scores for mixed-format tests

Dimensionality assessment provides test developers and users with a better understanding of how test scores make human abilities concrete. Issues dealt with by dimensionality assessment include, but are not restricted to, (a) whether unidimensionality holds; (b) the number of dimensions influencing test scores; and (c) the relationships among items, among underlying dimensions, and between items and dimensions. Results from dimensionality assessment allow test developers and users to carefully validate specific interpretations and uses of test scores. The widespread use of mixed-format tests complicates dimensionality assessment both conceptually and methodologically. This dissertation is the first to propose a framework tailored for exploratory type of dimensionality assessment for mixed-format tests. Based on real data from three large-scale mixed-format tests, this dissertation examined the performance of a number of popular and promising dimensionality assessment methods and procedures. Major findings were summarized, along with more extensive descriptions of the similarities and dissimilarities among methods and across different test subject areas, forms, and sample sizes. Limitations and possible further research topics were also discussed.