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ERIC Number: ED343918
Record Type: RIE
Publication Date: 1992-Jan
Pages: 21
Abstractor: N/A
Reference Count: N/A
The Variance of Rasch Ability Estimated from Partially-Known Item Parameters.
Mislevy, Robert J.
A closed form approximation is given for the variance of examinee proficiency estimates in the Rasch model for dichotomous items, under the condition that only estimates, rather than true values, of item difficulty parameters are available. The term that must be added to the usual response-sampling variance is inversely proportional to both the number of examinees in the item calibration sample and the length of the test. Illustrative numerical values suggest that the impact of uncertainty about Rasch item parameters on subsequent estimates of examinee proficiencies is less than has been observed in the two- and three-parameter logistic item response theory models. Two tables present approximate error variances, and an eight-item list of references is included. (Author/SLD)
Publication Type: Reports - Evaluative
Education Level: N/A
Audience: N/A
Language: English
Sponsor: Office of Naval Research, Arlington, VA. Cognitive and Neural Sciences Div.
Authoring Institution: Educational Testing Service, Princeton, NJ.
Identifiers: Ability Estimates; Dichotomous Variables; Item Parameters; Partial Knowledge (Tests); Rasch Model; Three Parameter Model; Two Parameter Model; Variance (Statistical)