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	Ordinal Item Response Theory	Differential Item Functioning (DIF)
Fagområde	Psykometri	Psykometri
Familie	Latent structure	Latent structure
Oprindelsesår	1969	1970s–1993
Ophavsperson	Fumiko Samejima (Graded Response Model, 1969); Gerhard Fischer & Georg Rasch lineage for partial credit	William H. Angoff and colleagues (ETS); systematized by Holland & Wainer
Type	Probabilistic latent trait model for ordered polytomous responses	Item-level bias detection
Oprindelig kilde	Samejima, F. (1969). Estimation of latent ability using a response pattern of graded scores. Psychometrika Monograph Supplement, 34(4, Pt. 2), 1–97.	Holland, P. W. & Wainer, H. (Eds.) (1993). Differential Item Functioning. Lawrence Erlbaum Associates. ISBN: 978-0805809589
Aliasser	polytomous IRT, ordinal IRT models, graded response models, ordinal latent trait models	DIF, item bias analysis, measurement non-equivalence, item-level measurement bias
Relaterede	6	5
Resumé	Ordinal item response theory (ordinal IRT) comprises a family of probabilistic models — most notably the Graded Response Model and the Partial Credit Model — that relate a respondent's standing on a latent trait to the probability of choosing each ordered response category on a polytomous item. It extends classical IRT beyond dichotomous items to the Likert-type and rating-scale items that dominate psychometric measurement.	Differential item functioning identifies test or survey items that behave differently for examinees from different groups — such as gender, ethnicity, or language background — after controlling for the underlying ability or trait being measured. DIF analysis is essential for fairness evaluation in educational testing and psychological scale development.