itemPar1PL {difR}R Documentation

Item parameter estimation for DIF detection using Rasch (1PL) model

Description

Fits the Rasch (1PL) model and returns related item parameter estimates.

Usage

 itemPar1PL(data, engine="ltm")
 

Arguments

data numeric: the data matrix.
engine character: the engine for estimating the 1PL model, either "ltm" (default) or "lme4".

Details

itemPar1PL permits to get item parameter estimates from the Rasch or 1PL model. The output is ordered such that it can be directly used with the general itemParEst command, as well as the methods of Lord (difLord) and Raju (difRaju) and Generalized Lord's (difGenLord) to detect differential item functioning.

The data is a matrix whose rows correspond to the subjects and columns to the items. Missing values are not allowed.

The estimation engine is set by the engine argument. By default (engine="ltm"), the Rasch model is fitted using marginal maximum likelihood, by means of the function rasch from the ltm package (Rizopoulos, 2006). The other option, engine="lme4", permits to fit the Rasch model as a generalized linear mixed model, by means of the glmer function of the lme4 package (Bates and Maechler, 2009).

Value

A matrix with one row per item and two columns, the first one with item parameter estimates and the second one with the related standard errors.

Author(s)

Sebastien Beland
Centre sur les Applications des Modeles de Reponses aux Items (CAMRI)
Universite du Quebec a Montreal
sebastien.beland.1@hotmail.com
David Magis
Research Group of Quantitative Psychology and Individual Differences
Katholieke Universiteit Leuven
David.Magis@psy.kuleuven.be, http://ppw.kuleuven.be/okp/home/
Gilles Raiche
Centre sur les Applications des Modeles de Reponses aux Items (CAMRI)
Universite du Quebec a Montreal
raiche.gilles@uqam.ca, http://www.er.uqam.ca/nobel/r17165/

References

Bates, D. and Maechler, M. (2009). lme4: Linear mixed-effects models using S4 classes. R package version 0.999375-31. http://CRAN.R-project.org/package=lme4

Rizopoulos, D. (2006). ltm: An R package for latent variable modelling and item response theory analyses. Journal of Statistical Software, 17, 1-25. URL: http://www.jstatsoft.org/v17/i05/

See Also

itemPar2PL, itemPar3PL, itemPar3PLconst, itemParEst, difLord, difRaju, difGenLord

Examples

# Loading of the verbal data
data(verbal)
 
# Getting item parameter estimates ('ltm' engine)
itemPar1PL(verbal[,1:24])

# Getting item parameter estimates ('lme4' engine) (remove #)
# itemPar1PL(verbal[,1:24], engine="lme4")

[Package difR version 1.1 Index]