irtoys-package
(Package: irtoys) :
Estimate and plot IRT models for binary responses
| Package: | irtoys | | Type: | Package | | Version: | 0.1.4 | | Date: | 2011-06-22 | | License: | GPL (>= 2) | | LazyLoad: | yes | | LazyData: | yes | | | Details Provides a common interface to the estimation of item parameters in IRT models for binary responses with three different programs (ICL, BILOG, and ltm, and a variety of functions useful with IRT models.
● Data Source:
CranContrib
● Keywords: models
● Alias: irtoys, irtoys-package
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mlebme
(Package: irtoys) :
Maximum likelihood and Bayes Modal estimation of ability
Estimates the value of the latent variable ("ability") for each person by direct optimization
● Data Source:
CranContrib
● Keywords: models
● Alias: mlebme
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tif
(Package: irtoys) :
Test information function
Returns the test information function (TIF) of the 3PL (1PL, 2PL) model. The TIF is the sum of the item information functions (IIF) in a test, and indicates the precision of measurement that can be achieved with the test at any value of the latent variable, bein inversely related to measurement variance.
● Data Source:
CranContrib
● Keywords: models
● Alias: tif
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From ICL output, read in estimates of item parameters. file must be a file produced with the write_latent_dist file command in ICL. Quadrature objects are used when estimating abilities with eap and for some of the scaling methods in sca.
● Data Source:
CranContrib
● Keywords: models
● Alias: read.qu.icl
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tsc
(Package: irtoys) :
True scores with standard errors
Computes the IRT true scores (test response function at the estimated ability) and an estimate of their standard error via the delta theorem, treating item parameters as known).
● Data Source:
CranContrib
● Keywords: models
● Alias: tsc
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qrs
(Package: irtoys) :
Quantiles of the ranked sum scores
A rough estimate of the values of the latent variable ("ability"). The sum scores (number of correct responses) are ranked, breaking ties at random. The ranks are divided by the sample size + 1, and the corresponding quantiles of the standard Normal distribution are returned. Used as default in the non-parametric IRF plots produced by npp in analogy to Jim Ramsay's TestGraf. Another possible use is in itf.
● Data Source:
CranContrib
● Keywords: models
● Alias: qrs
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sca
(Package: irtoys) :
Linear transformation of the IRT scale
Linearly transform a set of IRT parameters to bring them to the scale of another set of parameters. Four methods are implemented: Mean/Mean, Mean/Sigma, Lord-Stocking, and Haebara.
● Data Source:
CranContrib
● Keywords: models
● Alias: sca
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read.ip.icl
(Package: irtoys) :
Read in parameter estimates
From ICL output, read in estimates of item parameters. Invoked automatically when the model is estimated via irtoys. If that is not the case, file must be a file produced with the write_item_param file command in ICL.
● Data Source:
CranContrib
● Keywords: models
● Alias: read.ip.icl
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eap
(Package: irtoys) :
EAP estimation of ability
Estimates the expectation of the posterior distribution of the latent variable ("ability") for each person.
● Data Source:
CranContrib
● Keywords: models
● Alias: eap
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iif
(Package: irtoys) :
Item information function
The item information function (IIF) for the 3PL model can be computed as
● Data Source:
CranContrib
● Keywords: models
● Alias: iif
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providing 
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