itemPar1PL {difR} | R Documentation |
Fits the Rasch (1PL) model and returns related item parameter estimates.
itemPar1PL(data, engine="ltm")
data |
numeric: the data matrix. |
engine |
character: the engine for estimating the 1PL model, either "ltm" (default) or "lme4" . |
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).
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.
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/
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/
itemPar2PL
, itemPar3PL
, itemPar3PLconst
, itemParEst
, difLord
,
difRaju
, difGenLord
# 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")