skip to main content skip to footer

Sampling Variances and Covariances of Parameter Estimates in Item Response Theory ANCOVA IRT

Lord, Frederic M.; Wingersky, Marilyn S.
Publication Year:
Report Number:
ETS Research Report
Document Type:
Page Count:
Subject/Key Words:
Office of Naval Research, Analysis of Covariance (ANCOVA), Error of Measurement, Item Response Theory (IRT), Maximum Likelihood Statistics, Sampling, Statistical Analysis, Test Theory


A possible method is developed for computing the asymptotic sampling variance-covariance matrix of joint maximum likelihood estimates in item response theory when both item parameters and abilities are unknown. For a set of artificial data, results are compared with empirical values and with the variance-covariance matrices found by the usual formulas for the case where the abilities are known, or where the item parameters are known. The results are consistent with the conjecture that the new method is asymptotically correct except for errors due to grouping. (Author/PN). (46pp.)

Read More