Comparer des méthodes

	Oméga de McDonald polytomique	Alpha de Cronbach ordinal
Domaine	Psychométrie	Psychométrie
Famille	Latent structure	Latent structure
Année d'origine	1999 (omega); 2007 (polytomous extension)	2007
Auteur d'origine	Roderick P. McDonald (omega); extension for polytomous items by Zumbo, Gadermann & Zeisser	Zumbo, Gadermann, and Zeisser
Type	Reliability coefficient	Internal consistency reliability coefficient
Source fondatrice	Zumbo, B. D., Gadermann, A. M., & Zeisser, C. (2007). Ordinal versions of coefficients alpha and theta as measures of internal consistency for Likert rating scales. Journal of Modern Applied Statistical Methods, 6(1), 21–29.	Zumbo, B. D., Gadermann, A. M., & Zeisser, C. (2007). Ordinal versions of coefficients alpha and theta for Likert rating scales. Journal of Modern Applied Statistical Methods, 6(1), 21–29.
Alias	ordinal omega, omega for polytomous items, categorical omega, omega polychoric	alpha for ordinal data, polychoric alpha, ordinal reliability coefficient, alpha based on polychoric correlations
Apparentées	3	3
Résumé	Polytomous McDonald's omega estimates the internal consistency reliability of a scale composed of ordinal (polytomous) items — such as Likert-type responses — by computing omega from a factor model fitted to the polychoric correlation matrix rather than the Pearson correlation matrix, yielding estimates that are unbiased by the discreteness of item responses.	Ordinal Cronbach's alpha is a reliability coefficient computed from polychoric or polyserial correlations rather than Pearson correlations, making it appropriate for Likert-type and other ordinal item response data. It corrects the systematic downward bias that standard Cronbach's alpha produces when items are treated as continuous but are actually ordinal.