itemPar3PLconst {difR} | R Documentation |
Fits the 3PL model with constrained pseudo-guessing values and returns related item parameter estimates.
itemPar3PLconst(data, c=rep(0,ncol(data)))
data |
numeric: the data matrix. |
c |
numeric value or vector of constrained pseudo-guessing parameters. See Details. |
itemPar3PLconst
permits to get item parameter estimates from the 3PL model for which the pseudo-guessing parameters are constrained to some fixed values.
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 output is similar to that of itemPar2PL
method to fit the 2PL model; an additional column is included and holds the fixed pseudo-guessing
parameter values.
The data
is a matrix whose rows correspond to the subjects and columns to the items. Missing values are not allowed.
The argument c
can be either a single numeric value or a numeric vector of the same length of the number of items. In the former case, the pseudo-guessing
parameters are considered to be all identical to the given c
value; otherwise c
is directly used to constraint these parameters.
The constrained 3PL 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 six columns: the item discrimination a and difficulty estimates b, the corresponding standard errors se(a) and se(b), the covariances cov(a,b)and the constrained pseudo-guessing values c.
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
, itemPar2PL
, itemPar3PL
, itemParEst
, difLord
,
difRaju
, difGenLord
# Loading of the verbal data data(verbal) # Constraining all pseudo-guessing parameters to be equal to 0.05 itemPar3PLconst(verbal[,1:24], c=0.05) # Constraining pseudo-guessing values to 0.1 for the first 10 items, # and to 0.05 for the remaining ones itemPar3PLconst(verbal[,1:24], c=c(rep(0.1,10),rep(0.05,14)))