Omega for Mac

From Ed & Psych Associates:

A standalone Macintosh program to compute omega and omega hierarchical, measures of measurement precision or reliability, using standardized loadings from a bifactor confirmatory factor analysis. This software is based on a tutorial provided by Brunner, Nagy, and Wilhelm (2012).

As noted by Chen, Hayes, Carver, Laurenceau, and Zhang (2012), "for multidimensional constructs, the alpha coefficient is complexly determined, and McDonald's omega hierarchical (1999) provides a better estimate for the composite score and thus should be used" (p. 228). Bifactor (nested, direct hierarchical) models are prime examples where the variance of each observed measure is complexly determined and "omega hierarchical is an appropriate model-based reliability index when item response data are consistent with a bifactor structure" (Reise, 2012, p. 689). A prerequisite to using Omega is a good fitting, completely orthogonal bifactor model. Omega defines reliability in terms of the variance accounted for by all (i.e., general and group) constructs that underlie a scale score whereas omega hierarchical defines reliability in terms of the variance accounted for by a specific target construct (general or group) alone.