Does Item Homogeneity Indicate Internal Consistency or Item Redundancy in Psychometric Scales?

Abstract

Internal consistency or item homogeneity is often used for estimating intru-scale reliability. in terms of the item variances and covariances derived from a single occasion of measurement. While it is desirable that items in a psychometric scale measure something in common (i.e. exhibit unidimensionality), Hattic (1985) has indicated that there is still no satisfactory index. As Hattie (pp. 157 158) pointed out, a unidimcnsional scale (having an underlying Iatcnt trait), is not necessarily reliable, internally consistent or homogeneous. Hattie concluded that the frequent use of Cronbach’s alpha coefficient as a measure of uni-dimensionality is not justified.