itemPar2PL {difR} | R Documentation |
Item parameter estimation for DIF detection using 2PL model
Description
Fits the 2PL model and returns related item parameter estimates, standard errors and covariances between item parameters.
Usage
itemPar2PL(data)
Arguments
data |
numeric: the data matrix. |
Details
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 allowed but must be coded as NA
values. They are discarded for item parameter estimation.
The 2PL model is fitted using marginal maximum likelihood by means of the functions from the ltm
package (Rizopoulos, 2006).
Value
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.
Note
The 2PL model is fitted under the linear parametrization in ltm
, the covariance matrix is extracted with the vcov()
function, and final standard errors and covariances are derived by the Delta method. See Rizopoulos (2006) for further details, and the Note.pdf
document in the difR
package for mathematical details.
Author(s)
Sebastien Beland
Collectif pour le Developpement et les Applications en Mesure et Evaluation (Cdame)
Universite du Quebec a Montreal
sebastien.beland.1@hotmail.com, http://www.cdame.uqam.ca/
David Magis
Department of Psychology, University of Liege
Research Group of Quantitative Psychology and Individual Differences, KU Leuven
David.Magis@uliege.be, http://ppw.kuleuven.be/okp/home/
Gilles Raiche
Collectif pour le Developpement et les Applications en Mesure et Evaluation (Cdame)
Universite du Quebec a Montreal
raiche.gilles@uqam.ca, http://www.cdame.uqam.ca/
References
Magis, D., Beland, S., Tuerlinckx, F. and De Boeck, P. (2010). A general framework and an R package for the detection of dichotomous differential item functioning. Behavior Research Methods, 42, 847-862. doi: 10.3758/BRM.42.3.847
Rizopoulos, D. (2006). ltm: An R package for latent variable modelling and item response theory analyses. Journal of Statistical Software, 17, 1–25. doi: 10.18637/jss.v017.i05
See Also
itemPar1PL
, itemPar3PL
, itemPar3PLconst
, itemParEst
, difLord
, difRaju
,
Examples
## Not run:
# Loading of the verbal data
data(verbal)
# Getting item parameter estimates
itemPar2PL(verbal[,1:24])
## End(Not run)