itemRescale {difR}R Documentation

Rescaling item parameters by equal means anchoring

Description

Rescale the item parameters from one data set to the scale of the parameters from another data set, using equal means anchoring.

Usage

 itemRescale(mR, mF, items=1:nrow(mR))
 

Arguments

mR numeric: a matrix of item parameter estimates (one row per item) which constitutes the reference scale. See Details.
mF numeric: a matrix of item parameter estimates (one row per item) which have to be rescaled. See Details.
items a numeric vector of integer values specifying which items are used for equal means anchoring. See Details.

Details

The matrices mR and mF must have the same format as the output of the command itemParEst and one the possible models (1PL, 2PL, 3PL or constrained 3PL). The number of columns therefore equals two, five, nine or six, respectively.

Rescaling is performed by equal means anchoring (Cook and Eignor, 1991). The items involved in the anchoring process are specified by means of their row number in either mR or mF, and are passed through the items argument.

itemrescale primarily serves as a routine for item purification in Lord (difLord) and Raju (difRaju) Generalized Lord's (difGenLord)methods of DIF identification (Candell and Drasgow, 1988).

Value

A matrix of the same format as mF with the rescaled item parameters.

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

Candell, G.L. and Drasgow, F. (1988). An iterative procedure for linking metrics and assessing item bias in item response theory. Applied Psychological Measurement, 12, 253-260.

Cook, L. L. and Eignor, D. R. (1991). An NCME instructional module on IRT equating methods. Educational Measurement: Issues and Practice, 10, 37-45.

See Also

itemPar1PL, itemPar2PL, itemPar3PL, itemPar3PLconst, difLord, difRaju, difGenLord

Examples

# Loading of the verbal data
data(verbal)
attach(verbal)

# Splitting the data set into reference and focal groups
nF<-sum(Gender)
nR<-nrow(verbal)-nF
data.ref<-verbal[,1:24][order(Gender),][1:nR,]
data.focal<-verbal[,1:24][order(Gender),][(nR+1):(nR+nF),]

# Estimating item parfameters in each data set with 1PL model
mR<-itemPar1PL(data.ref)
mF<-itemPar1PL(data.focal)

# Rescaling focal group item parameters, using all items for anchoring
itemRescale(mR, mF)

# Rescaling focal group item parameters, using the first 10 items for 
# anchoring
itemRescale(mR, mF, items=1:10)

# Estimating item parfameters in each data set with 2PL model
mR<-itemPar2PL(data.ref)
mF<-itemPar2PL(data.focal)

# Rescaling focal group item parameters, using all items for anchoring
itemRescale(mR, mF)

[Package difR version 1.1 Index]