Evaluating Statistical Targets for Assembling Parallel Mixed-Format Test Forms

Test assembly is the process of selecting items from an item pool to form one or more new test forms. Often new test forms are constructed to be parallel with an existing (or an ideal) test. Within the context of item response theory, the test information function (TIF) or the test characteristic curve (TCC) are commonly used as statistical targets to obtain this parallelism. In a recent study, Ali and van Rijn proposed combining the TIF and TCC as statistical targets, rather than using only a single statistical target. In this article, we propose two new methods using this combined approach, and compare these methods with single statistical targets for the assembly of mixed-format tests. In addition, we introduce new criteria to evaluate the parallelism of multiple forms. The results show that single statistical targets can be problematic, while the combined targets perform better, especially in situations with increasing numbers of polytomous items. Implications of using the combined target are discussed.