itemPar2PL {difR} | R Documentation |
Fits the 2PL model and returns related item parameter estimates.
itemPar2PL(data)
data |
numeric: the data matrix. |
itemPar2PL
permits to get item parameter estimates from the 2PL 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 2PL model is fitted using marginal maximum likelihood by means of the functions from the ltm
package (Rizopoulos, 2006).
A matrix with one row per item and five columns: the estimates of item discrimination a and difficulty b parameters, the related standard errors se(a) and se(b), and the covariances cov(a,b), in this order.
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/
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/
itemPar1PL
, itemPar3PL
, itemPar3PLconst
, itemParEst
, difLord
,
difRaju
, difGenLord
# Loading of the verbal data data(verbal) # Getting item parameter estimates itemPar2PL(verbal[,1:24])