On Estimating the Reliability of Composite Indexes Through Factor Analysis

The rationale for Heise and Bohrnstedt's index of reliability, omega, is restated in terms of the models of classical measurement theory and factor analysis. Although omega is the best available internal-consistency estimate of reliability, its value is generally lower than a composite scale's true reliability in the classical measurement model. Under quite foreseeable circumstances, it may be appreciably lower. Some implications for forming indexes through factor analysis are discussed.