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PROC NLMIXED: For Estimating Parameters of IRT Models


Applied Psychological Measurement Volume 36, Number 1, ISSN 0146-6216


The PROC NLMIXED procedure in Statistical Analysis System can be used to estimate parameters of item response theory (IRT) models. The data for this procedure are set up in a particular format called the "long format." The long format takes a substantial amount of time to execute the program. This article describes a format called the "wide format" to estimate parameters of an IRT model more efficiently. The wide format substantially reduces execution time for models with few parameters. But the time savings decline as the number of parameters increases. (Contains 5 tables.)


Nandakumar, R. & Hotchkiss, L. (2012). PROC NLMIXED: For Estimating Parameters of IRT Models. Applied Psychological Measurement, 36(1), 60-63. Retrieved August 20, 2019 from .

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