A Review of DIMPACK Version 1.0

Abstract

DIMPACK Version 1.0 for assessing test dimensionality based on a nonparametric conditional covariance approach is reviewed. This software was originally distributed by Assessment Systems Corporation and now can be freely accessed online. The software consists of Windows-based interfaces of three components: DIMTEST, DETECT, and CCPROX/HAC, which conduct hypothesis test for unidimensionality, cluster items, and perform hierarchical cluster analysis, respectively. Two simulation studies were conducted to evaluate the software in confirming test unidimensionality (a Type I error study) and detecting multidimensionality (a statistical power study). The results suggested that different data always be used in selecting assessment subtest items independent of calculating the DIMTEST statistic. The Type I error rate was excessively inflated otherwise. The statistical power was found low when sample size was small or the dimensions were highly correlated. It is suggested that some major changes be made to the software before it can be successfully useful among practitioners.