Dimensionality of Tests: Methodology

Abstract

It is important that a score based on a set of items be unidimensional – that is, there is only one latent trait underlying the items. The notion of unidimensionality can be considered in traditional test theory and item response models in terms of the relations between items, and it can also be considered in terms of the cognitive processes involved in answering items. The more recent developments of Stout and colleagues has provided important advances in methods to assess unidimensionality, and the diagnostics procedures now available can greatly improve the development of unidimensional sets of items.