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Additionally to reporting Cronbachs Alpha, I would like to report McDonals Omega for each scale of my survey. I know that there are two ways to get Omega in R - either with the psych command omega() which is for exploratory analysis or with reliability-command in semtools which is for confirmatory analysis. Because I have difficulties calculating the latter, I would like to know whether the results of both omegas are identical in terms of value?

Thanks in advance!

Carolin

Carolin
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Part of the problem is that there are two different omega coefficients. Omega_h and Omega_t. I just checked semTools and they seem to report omega_t (which they label as omega).

psych reports both. With the example data set from semTools, the answers are similar, but not identical. I suspect the difference is the psych version allows cross loadings and the sem version does not.

reliability(fit) visual textual speed total alpha 0.6261171 0.8827069 0.6884550 0.7604886 omega 0.6253180 0.8851754 0.6877600 0.8453351 omega2 0.6253180 0.8851754 0.6877600 0.8453351 omega3 0.6120052 0.8850608 0.6858417 0.8596204 avevar 0.3705589 0.7210163 0.4244883 0.5145874

summary(omega(HolzingerSwineford1939[7:15],covar=TRUE))

Omega Alpha: 0.76 G.6: 0.81 Omega Hierarchical: 0.44 Omega H asymptotic: 0.52 Omega Total 0.85

... Total, General and Subset omega for each subset g F1* F2* F3* Omega total for total scores and subscales 0.85 0.89 0.65 0.71 Omega general for total scores and subscales 0.44 0.27 0.24 0.17 Omega group for total scores and subscales 0.35 0.62 0.40 0.54

For a discussion of various estimates of reliability see the article on PsyArXiv preprints: reliability from Alpha to Omega preprint of reliability article available from psyArXiv

William Revelle
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