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	McDonald's Omega (ω) tillförlitlighetskoefficient	Raschmodell
Ämnesområde	Psykometri	Psykometri
Familj	Latent structure	Latent structure
Ursprungsår	1999	1960
Upphovsperson	Roderick P. McDonald	Georg Rasch
Typ	Reliability coefficient / latent variable model	Item Response Theory / Latent trait model
Ursprungskälla	McDonald, R. P. (1999). Test Theory: A Unified Treatment. Lawrence Erlbaum Associates. ISBN: 978-0805830750	Rasch, G. (1960). Probabilistic Models for Some Intelligence and Attainment Tests. Danish Institute for Educational Research, Copenhagen.
Alias	omega reliability, ω coefficient, omega total, omega hierarchical	1PL IRT, one-parameter logistic model, Rasch Modeli — 1PL IRT, 1PL model
Närliggande	6	6
Sammanfattning	McDonald's omega is a factor-analysis-based reliability coefficient introduced by Roderick P. McDonald (1999) that quantifies the internal consistency of a composite score without requiring the restrictive assumption that all items contribute equally to the latent factor. It yields two complementary indices: ω_total, which captures overall reliability of the sum score, and ω_hierarchical (ωh), which reports how much of the composite's variance is explained specifically by a single general factor.	The Rasch model, introduced by Georg Rasch in 1960, is the simplest member of the Item Response Theory (IRT) family. It assigns a single difficulty parameter to each test item and places both item difficulties and person abilities on the same logit scale, enabling direct, sample-independent comparison of items and persons.