Despite the current need for reliable and valid test instruments in different countries in order to monitor the sign language acquisition of deaf children, very few tests are commercially available that offer strong evidence for their psychometric properties. This mirrors the current state of affairs for many sign languages, where very little…

This simulation study considered the effects on statistical measures of test dimensionality that result from systematic sampling variation in both a single- and a double-trait assessment model. Results suggest that there are distinct psychological and psychometric states of test dimensionality, and that psychometric unidimensionality may be…

Violations of item unidimensionality on language tests produced distorted estimates of person ability, and violations of person unidimensionality produced distorted estimates of item difficulty. The Bejar Method was sensitive to such distortions. (Author)