An Assessment of Stout's Index of Essential Unidimensionality

Abstract

A simulation study was conducted to evaluate the dependability of Stout's T index of unidimensionality as used in his DIMTEST procedure. DIMTEST was found to dependably provide indications of unidimensionality, to be reasonably robust, and to allow for a practical demar cation between one and many dimensions. The proce dure was not affected by the method used to identify the initial subset of unidimensional items. It was, how ever, found to be sensitive to whether the multidimen sional data arose from a compensatory model or a partially compensatory model. DIMTEST failed when the matrix of tetrachoric correlations was non-Gramian and hence is not appropriate in such cases.