eqc {equateIRT}

Extract Equating Coefficients

Description

eqc is a generic function which extracts the equating coefficients.

Usage

eqc(x, ...)

## S3 method for class 'eqc'
eqc(x, ...)

## S3 method for class 'eqclist'
eqc(x, link = NULL, ...)

## S3 method for class 'ceqc'
eqc(x, ...)

## S3 method for class 'ceqclist'
eqc(x, link = NULL, path = NULL, ...)

## S3 method for class 'meqc'
eqc(x, link = NULL, path = NULL, ...)

Arguments

x

object of the class eqc returned by function direc or of the class eqclist returned by function alldirec or of the class ceqc and ceqclist returned by function chainec or of the class meqc returned by function bisectorec.

link

a character string with the names of the two forms being linked separated by a dot (e.g. "test1.test3").

path

a character string with the names of the forms that constitute the path separated by a dot (e.g. "test1.test2.test3").

...

further arguments passed to or from other methods.

Value

A data frame containing the equating coefficients for every link and path.

Author(s)

Michela Battauz

See Also

alldirec, bisectorec, chainec, direc, modIRT

Examples

# the following code uses item parameter estimates previously obtained
# for examples that start from item response data see function modIRT

# two-parameter logistic model
data(est2pl)
test<-paste("test", 1:5, sep = "")
mod2pl <- modIRT(coef = est2pl$coef, var = est2pl$var, names = test, display = FALSE)
# direct equating coefficients between forms 1 and 2 using the Haebara method
l12 <- direc(mods = mod2pl, which = c(1,2), method = "Haebara")
# all direct equating coefficients using the Haebara method
direclist2pl <- alldirec(mods = mod2pl, method = "Haebara")
# compute all chain equating coefficients of length 3
chainec3 <- chainec(r = 3, direclist = direclist2pl)
# compute chain equating coefficients for path 1,2,3,4
pth1 <- paste("test", 1:4, sep = "")
chainec1 <- chainec(direclist = direclist2pl, pths = pth1)
# compute chain equating coefficients for path 1,5,4
pth2 <- c(paste("test", c(1,5,4), sep = ""))
chainec2 <- chainec(direclist = direclist2pl, pths = pth2)
# create a list of objects of class ceqc
ecall <- c(chainec1, chainec2)
# compute bisector and weighted bisector coefficients
allec <- bisectorec(ecall = ecall, weighted = TRUE, unweighted = TRUE)

# extract equating coefficients
eqc(l12)
eqc(direclist2pl)
eqc(direclist2pl, link = "test1.test2")
eqc(chainec3)
eqc(chainec3, link = "test1.test3")
eqc(allec)
eqc(allec, path = "bisector")