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	Item Response Theory (IRT)	Vertical Scaling
Ämnesområde	Psykometri	Education
Familj	Latent structure	Latent structure
Ursprungsår	1952–1968	2014
Upphovsperson	Frederic M. Lord (and Allan Birnbaum for the 2PL/3PL models)	Educational measurement tradition (Thurstone; Kolen & Brennan synthesis)
Typ	Probabilistic measurement model	Construction of a single developmental score scale spanning multiple grades
Ursprungskälla	Lord, F. M. & Novick, M. R. (1968). Statistical Theories of Mental Test Scores. Addison-Wesley.	Kolen, M. J., & Brennan, R. L. (2014). Test Equating, Scaling, and Linking: Methods and Practices (3rd ed.). Springer. ISBN: 9781493903160
Alias	IRT, latent trait theory, item characteristic curve theory, modern test theory	Developmental Scaling, Vertical Linking, Cross-Grade Scaling, Growth Scale Construction
Närliggande	5	4
Sammanfattning	Item response theory models the probability that a respondent answers an item correctly (or endorses it) as a function of the respondent's latent trait level and the item's own statistical properties — difficulty, discrimination, and guessing. Unlike classical test theory, IRT places persons and items on the same scale, yielding measurement that is sample-independent for items and test-independent for persons.	Vertical scaling places tests written for different grade levels onto a single continuous score scale so that growth from one grade to the next can be measured in common units. Unlike horizontal equating, which links alternate forms intended to be interchangeable, vertical scaling deliberately links tests of differing difficulty and content to build a developmental continuum spanning, for example, grades 3 through 8. It is the measurement foundation that lets a fourth-grade and a fifth-grade score be subtracted to express how much a student grew.