Marengo, D., Miceli, R., & Settanni, M.
Do mixed item formats threaten test unidimensionality? Results from a standardized math achievement test
Numerous studies suggest that while multiple-choice (MC) and constructed-response (CR) items for the most part measure the same construct, a residual local dependence among CR items producing multidimensionality can be observed in mixed-format tests. The main aim of this study was to investigate the existence of format-related multidimensionality in a standardized math test administered as part of the Italian statewide educational assessment program implemented by INVALSI in 2012. Working within the framework of Item Response Theory (IRT), we tested the hypothesis that a bidimensional compensatory IRT model letting MC and CR items load on a common latent dimension, and the CR items additionally load on an a secondary dimension would be more appropriate than a unidimensional model for the examined test. The existence of a secondary CR ability dimension was not fully supported by the results. Specific considerations for practitioners and future research are presented.Back