import.ltm: Import Item Parameters Estimates and Covariance Matrices from...

In equateIRT: IRT Equating Methods

Import Item Parameters Estimates and Covariance Matrices from IRT Software

Description

Import estimated item parameters and covariance matrix from the R packages ltm and mirt, and from external software IRTPRO and flexMIRT.

Usage

import.ltm(mod, display = TRUE, digits = 4) 

import.mirt(mod, display = TRUE, digits = 3) 

import.irtpro(fnamep, fnamev = NULL, fnameirt = NULL, display = TRUE, digits = 2) 

import.flexmirt(fnamep, fnamev = NULL, fnameirt = NULL, display = TRUE, digits = 2) 

Arguments

mod	output object from functions rasch, ltm, or tpm of the ltm package or from function mirt of the mirt package.
display	logical; if TRUE coefficients and standard errors are printed.
digits	integer indicating the number of decimal places to be used if display is TRUE.
fnamep	name of the file containing the estimated item parameters. Typically, -prm.txt.
fnamev	name of the file containing the covariance matrix of the estimated item parameters. Typically, -cov.txt.
fnameirt	name of the file containing additional information to link item parameters with the covariance matrix. Typically, -irt.txt.

Details

Item parameters are imported with the parameterization used by the software to estimate the IRT model. The usual IRT parameterization can be obtained later by using function modIRT.

Value

A list with components

coef	item parameter estimates.
var	covariance matrix of item parameter estimates.

Author(s)

Michela Battauz

References

Battauz, M. (2015). equateIRT: An R Package for IRT Test Equating. Journal of Statistical Software, 68, 1–22.

Cai L. (2013). FlexMIRT version 2: Flexible Multilevel Multidimensional Item Analysis and Test Scoring [Computer Software]. Chapel Hill, NC: Vector Psychometric Group.

Cai, L., du Toit, S. H. C., Thissen, D. (2011). IRTPRO: Flexible, multidimensional, multiple categorical IRT modeling [Computer software]. Chicago: Scientific Software International.

Chalmers, R. P. (2012). mirt: A Multidimensional Item Response Theory Package for the R Environment. Journal of Statistical Software, 48, 1–29.

Rizopoulos, D. (2006). ltm: an R package for latent variable modelling and item response theory analyses. Journal of Statistical Software, 17, 1–25.

See Also

modIRT

Examples

#====================
# from package ltm
library(ltm)

# one-parameter logistic model
mod1pl <- rasch(LSAT)
est.mod1pl <- import.ltm(mod1pl)
est.mod1pl

# two-parameter logistic model
mod2pl <- ltm(LSAT ~ z1)
est.mod2pl <- import.ltm(mod2pl)
est.mod2pl

#====================
# from package mirt
library(mirt)

# one-parameter logistic model
data(LSAT, package = "ltm")
val <- mirt(LSAT, 1, SE = TRUE, pars = "values")
cnstr <- val[val$name == "a1",]$parnum
mod1pl.m <- mirt(LSAT, 1, SE = TRUE, SE.type = 'Richardson', constrain = list(cnstr))
est.mod1pl.m <- import.mirt(mod1pl.m, digits = 4)
est.mod1pl.m

# two-parameter logistic model
data(LSAT, package = "ltm")
mod2pl.m <- mirt(LSAT, 1, SE = TRUE, SE.type = 'Richardson')
est.mod2pl.m <- import.mirt(mod2pl.m, display = FALSE)
est.mod2pl.m

equateIRT documentation built on Aug. 8, 2022, 5:08 p.m.