linking_2groups: Linking Two Groups

In alexanderrobitzsch/sirt: Supplementary Item Response Theory Models

Linking Two Groups

Description

This function performs (robust) Haebara linking or Stocking-Lord for two groups in the 2PL model. There is also an option for simultaneous estimation in which joint item parameters should also be estimated.

Usage

linking_2groups(pars, method, type="asymm", pow=2, eps=0.001, simultan=FALSE,
     Theta=seq(-6, 6, len=101), wgt=NULL, par_init=NULL, optimizer="nlminb",
     control_optimizer=list())

Arguments

pars	Matrix containing item parameters that must have columns with names a1, b1, a2, and b2.
method	Linking method. Can be SL (Stocking-Lord) or Hae (Haebara).
type	Type of linking function. Can be "asymm" or "symm" for asymmetric or symmetric linking, respectively.
pow	Power used in the loss function. The values should be larger than or equal than zero. The default values is 2.
eps	Tuning parameter in numerical differentiation
simultan	Logical indicating whether joint item parameters should be simultaneously estimated
Theta	Theta grid
wgt	Weights for theta grid
par_init	Initial vector for parameters
optimizer	Chosen optimizer. Can be "nlminb" or "optim".
control_optimizer	Control arguments for optimizer

Value

List with following entries

par	Estimated linking parameters
$...$	More values

Examples

## Not run: 
#############################################################################
# EXAMPLE 1: data.ex16 from TAM package
#############################################################################

#- extract dataset
data(data.ex16, package="TAM")
dat <- data.ex16
items <- colnames(dat)[-c(1,2)]

# fit grade 1
rdat1 <- TAM::tam_remove_missings( dat[ dat$grade==1, ], items=items )
mod1 <- sirt::rasch.mml2( dat=rdat1$resp[, rdat1$items], est.a=1:length(rdat1$items) )

# fit grade 2
rdat2 <- TAM::tam_remove_missings( dat[ dat$grade==2, ], items=items )
mod2 <- sirt::rasch.mml2( dat=rdat2$resp[, rdat2$items], est.a=1:length(rdat2$items) )

# merge item parameters of separate scalings
item1 <- mod1$item[, c("item", "a","b") ]
colnames(item1)[2:3] <- c("a1","b1")
item2 <- mod2$item[, c("item", "a","b") ]
colnames(item2)[2:3] <- c("a2","b2")
pars <- merge(x=item1, y=item2, by="item")

# choose theta grid
Theta <- seq(-6,6, len=101)
wgt <- sirt::sirt_dnorm_discrete(x=Theta, mean=0, sd=2)

#- robust Haebara linking with powers 0.5 or 0 and different types
res1 <- sirt::linking_2groups(pars=pars, method="Hae", type="asymm",
              Theta=Theta, wgt=wgt, pow=0.5, eps=0.001 )
res2 <- sirt::linking_2groups(pars=pars, method="Hae", type="symm",
              Theta=Theta, wgt=wgt, pow=0, eps=0.01 )
res1$par  # linking parameter estimate
res2$par

## End(Not run)

alexanderrobitzsch/sirt documentation built on June 11, 2025, 3:21 p.m.