AN ASSESSMENT OF STOUTS INDEX OF ESSENTIAL UNIDIMENSIONALITY

A simulation study was conducted to evaluate the dependability of Stou t's T index of unidimensionality as used in his DIMTEST procedure. DIM TEST was found to dependably provide indications of unidimensionality, to be reasonably robust, and to allow for a practical demarcation bet ween one and many dimensions. The procedure was not affected by the me thod used to identify the initial subset of unidimensional items. It w as, however, found to be sensitive to whether the multidimensional dat a arose from a compensatory model or a partially compensatory model. D IMTEST failed when the matrix of tetrachoric correlations was non-Gram ian and hence is not appropriate in such cases.