#############################################################################
# EXAMPLE 1: Reading dataset
#############################################################################
data(data.read)
dat <- data.read
I <- ncol(dat) # number of items
# Rasch model
mod1 <- rasch.mml2( dat )
summary(mod1)
plot( mod1 ) # plot all items
# title 'Rasch model', display curves from -3 to 3 only for items 1, 5 and 8
plot(mod1, main="Rasch model Items 1, 5 and 8", xlim=c(-3,3) , items=c(1,5,8) )
# Rasch model with constraints on item difficulties
# set item parameters of A1 and C3 equal to -2
constraints <- data.frame( c("A1","C3") , c(-2,-2) )
mod1a <- rasch.mml2( dat , constraints=constraints)
summary(mod1a)
# estimate equal item parameters for 1st and 11th item
est.b <- 1:I
est.b[11] <- 1
mod1b <- rasch.mml2( dat , est.b = est.b )
summary(mod1b)
# estimate Rasch model with skew trait distribution
mod1c <- rasch.mml2( dat , distribution.trait="smooth3")
summary(mod1c)
# 2PL model
mod2 <- rasch.mml2( dat , est.a = 1:I )
summary(mod2)
plot(mod2) # plot 2PL item response curves
# extract individual likelihood
llmod2 <- IRT.likelihood(mod2)
str(llmod2)
library(CDM)
# model comparisons
CDM::IRT.compareModels(mod1, mod1c, mod2 )
anova(mod1,mod2)
# assess model fit
smod1 <- IRT.modelfit(mod1)
smod2 <- IRT.modelfit(mod2)
IRT.compareModels(smod1, smod2)
# set some bounds for a and b parameters
mod2a <- rasch.mml2( dat , est.a=1:I , min.a = .7 , max.a=2 , min.b = -2 )
summary(mod2a)
# 3PL model
mod3 <- rasch.mml2( dat , est.a = 1:I , est.c = 1:I ,
mmliter = 400 # maximal 400 iterations
)
summary(mod3)
# 3PL model with fixed guessing paramters of .25 and equal slopes
mod4 <- rasch.mml2( dat , fixed.c = rep( .25 , I ) )
summary(mod4)
# 3PL model with equal guessing paramters for all items
mod5 <- rasch.mml2( dat , est.c = rep(1, I ) )
summary(mod5)
# difficulty + guessing model
mod6 <- rasch.mml2( dat , est.c = 1:I )
summary(mod6)
# 4PL model
mod7 <- rasch.mml2( dat , est.a = 1:I , est.c=1:I , est.d = 1:I ,
min.d = .95 , max.c = .25)
# set minimal d and maximal c parameter to .95 and .25
summary(mod7)
# constrained 4PL model
# equal slope, guessing and slipping parameters
mod8 <- rasch.mml2( dat ,est.c=rep(1,I) , est.d = rep(1,I) )
summary(mod8)
# estimation of an item response model with an
# uniform theta distribution
theta.k <- seq( 0.01 , .99 , len=20 )
trait.weights <- rep( 1/length(theta.k) , length(theta.k) )
mod9 <- rasch.mml2( dat , theta.k=theta.k , trait.weights = trait.weights ,
normal.trait=FALSE , est.a = 1:12 )
summary(mod9)
#############################################################################
# EXAMPLE 2: Longitudinal data
#############################################################################
data(data.long)
dat <- data.long[,-1]
# define Q loading matrix
Qmatrix <- matrix( 0 , 12 , 2 )
Qmatrix[1:6,1] <- 1 # T1 items
Qmatrix[7:12,2] <- 1 # T2 items
# define restrictions on item difficulties
est.b <- c(1,2,3,4,5,6, 3,4,5,6,7,8)
mu.fixed <- cbind(1,0)
# set first mean to 0 for identification reasons
# Model 1: 2-dimensional Rasch model
mod1 <- rasch.mml2( dat , Qmatrix=Qmatrix , miterstep=4,
est.b = est.b , mu.fixed = mu.fixed , mmliter=30 )
summary(mod1)
plot(mod1)
## Plot function is only applicable for unidimensional models
#############################################################################
# SIMULATED EXAMPLE 3
# one group, estimation of alpha parameter in the generalized logistic model
#############################################################################
# simulate theta values
set.seed(786)
N <- 1000 # number of persons
theta <- rnorm( N , sd =1.5 ) # N persons with SD 1.5
b <- seq( -2 , 2 , len=15)
# simulate data
dat <- sim.raschtype( theta = theta , b = b , alpha1 = 0 , alpha2 = -0.3 )
# estimating alpha parameters
mod1 <- rasch.mml2( dat , est.alpha = TRUE , mmliter=30 )
summary(mod1)
plot(mod1)
# fixed alpha parameters
mod1b <- rasch.mml2( dat , est.alpha = FALSE , alpha1=0 , alpha2=-.3 )
summary(mod1b)
# estimation with equal alpha parameters
mod1c <- rasch.mml2( dat , est.alpha = TRUE , equal.alpha=TRUE )
summary(mod1c)
# Ramsay QM
mod2a <- rasch.mml2( dat , irtmodel ="ramsay.qm" )
summary(mod2a)
# Ramsay QM with estimated K parameters
mod2b <- rasch.mml2( dat , irtmodel ="ramsay.qm" , est.K=1:15 , mmliter=30)
summary(mod2b)
plot(mod2b)
# nonparametric estimation of monotone item response curves
mod3a <- rasch.mml2( dat , irtmodel ="npirt" , mmliter =100 ,
theta.k = seq( -3 , 3 , len=10) ) # evaluations at 10 theta grid points
# nonparametric ICC of first 4 items
round( t(mod3a$pjk)[1:4,] , 3 )
summary(mod3a)
plot(mod3a)
# nonparametric IRT estimation without monotonicity assumption
mod3b <- rasch.mml2( dat , irtmodel ="npirt" , mmliter =10 ,
theta.k = seq( -3 , 3 , len=10) , npirt.monotone=FALSE)
plot(mod3b)
# B-Spline estimation of ICCs
library(splines)
mod3c <- rasch.mml2( dat , irtmodel ="npirt" ,
npformula = "y~bs(theta,df=3)" , theta.k = seq(-3,3,len=15) )
summary(mod3c)
round( t(mod3c$pjk)[1:6,] , 3 )
plot(mod3c)
# estimation of quadratic item response functions: ~ theta + I( theta^2)
mod3d <- rasch.mml2( dat , irtmodel ="npirt" ,
npformula = "y~theta + I(theta^2)" )
summary(mod3d)
plot(mod3d)
# estimation of a stepwise ICC function
# ICCs are constant on the theta domains: [-Inf,-1], [-1,1], [1,Inf]
mod3e <- rasch.mml2( dat , irtmodel ="npirt" ,
npformula = "y~I(theta>-1 )+I(theta>1)" )
summary(mod3e)
plot(mod3e , xlim=c(-2.5,2.5) )
# 2PL model
mod4 <- rasch.mml2( dat , est.a=1:15)
summary(mod4)
#############################################################################
# SIMULATED EXAMPLE 4
# two groups, estimation of generalized logistic model
#############################################################################
# simulate generalized logistic Rasch model in two groups
set.seed(8765)
N1 <- 1000 # N1=1000 persons in group 1
N2 <- 500 # N2= 500 persons in group 2
dat1 <- sim.raschtype( theta = rnorm( N1 , sd = 1.5 ) , b = b ,
alpha1 = -0.3 , alpha2=0)
dat2 <- sim.raschtype( theta = rnorm( N2 , mean=-.5 , sd =.75) ,
b = b , alpha1 = -0.3 , alpha2=0)
dat1 <- rbind( dat1 , dat2 )
group <- c( rep(1,N1) , rep(2,N2))
mod1 <- rasch.mml2( dat1 , parm.conv=.0001 , group=group , est.alpha = TRUE )
summary(mod1)
#############################################################################
# SIMULATED EXAMPLE 5: Multidimensional model
#############################################################################
#***
# (1) simulate data
set.seed(785)
library(mvtnorm)
N <- 500
theta <- mvtnorm::rmvnorm( N,mean=c(0,0), sigma=matrix( c(1.45,.5,.5,1.7) , 2 , 2 ))
I <- 10
# 10 items load on the first dimension
p1 <- plogis( outer( theta[,1] , seq( -2 , 2 , len=I ) , "-" ) )
resp1 <- 1 * ( p1 > matrix( runif( N*I ) , nrow=N , ncol=I ) )
# 10 items load on the second dimension
p1 <- plogis( outer( theta[,2] , seq( -2 , 2 , len=I ) , "-" ) )
resp2 <- 1 * ( p1 > matrix( runif( N*I ) , nrow=N , ncol=I ) )
#Combine the two sets of items into one response matrix
resp <- cbind(resp1,resp2)
colnames(resp) <- paste("I" , 1:(2*I), sep="")
dat <- resp
# define Q-matrix
Qmatrix <- matrix( 0 , 2*I , 2 )
Qmatrix[1:I,1] <- 1
Qmatrix[1:I+I,2] <- 1
#***
# (2) estimation of models
# 2-dimensional Rasch model
mod1 <- rasch.mml2( dat , Qmatrix=Qmatrix )
summary(mod1)
# 2-dimensional 2PL model
mod2 <- rasch.mml2( dat , Qmatrix=Qmatrix , est.a = 1:(2*I) )
summary(mod2)
# estimation with some fixed variances and covariances
# set variance of 1st dimension to 1 and
# covariance to zero
variance.fixed <- matrix( cbind(c(1,1) , c(1,2) , c(1,0)) ,
byrow=FALSE , ncol= 3 )
mod3 <- rasch.mml2( dat , Qmatrix=Qmatrix , variance.fixed = variance.fixed )
summary(mod3)
# constraints on item difficulties
# useful for example in longitudinal linking
est.b <- c( 1:I , 1:I )
# equal indices correspond to equally estimated item parameters
mu.fixed <- cbind( 1 , 0 )
mod4 <- rasch.mml2( dat, Qmatrix=Qmatrix, est.b = est.b , mu.fixed = mu.fixed )
summary(mod4)
#############################################################################
# SIMULATED EXAMPLE 6: Two booklets with same items but with item context effects.
# Therefore, item slopes and item difficulties are assumed to be shifted in the
# second design group.
#############################################################################
#***
# simulate data
set.seed(987)
I <- 10 # number of items
# define person design groups 1 and 2
n1 <- 700
n2 <- 1500
# item difficulties group 1
b1 <- seq(-1.5,1.5,length=I)
# item slopes group 1
a1 <- rep(1, I)
# simulate data group 1
dat1 <- sim.raschtype( rnorm(n1) , b=b1 , fixed.a=a1 )
colnames(dat1) <- paste0("I" , 1:I , "des1" )
# group 2
b2 <- b1 - .15
a2 <- 1.1*a1
# Item parameters are slightly transformed in the second group
# compared to the first group. This indicates possible item context effects.
# simulate data group 2
dat2 <- sim.raschtype( rnorm(n2) , b=b2 , fixed.a=a2 )
colnames(dat2) <- paste0("I" , 1:I , "des2" )
# define joint dataset
dat <- matrix( NA , nrow=n1+n2 , ncol=2*I)
colnames(dat) <- c( colnames(dat1) , colnames(dat2) )
dat[ 1:n1 , 1:I ] <- dat1
dat[ n1 + 1:n2 , I + 1:I ] <- dat2
# define group identifier
group <- c( rep(1,n1) , rep(2,n2) )
#***
# Model 1: Rasch model two groups
itemindex <- rep( 1:I , 2 )
mod1 <- rasch.mml2( dat , group=group , est.b=itemindex )
summary(mod1)
#***
# Model 2: two item slope groups and designmatrix for intercepts
designmatrix <- matrix( 0 , 2*I , I+1)
designmatrix[ ( 1:I )+ I,1:I] <- designmatrix[1:I ,1:I] <- diag(I)
designmatrix[ ( 1:I )+ I,I+1] <- 1
mod2 <- rasch.mml2( dat , est.a=rep(1:2,each=I) , designmatrix=designmatrix )
summary(mod2)
#############################################################################
# EXAMPLE 7: PIRLS dataset with missing responses
#############################################################################
data(data.pirlsmissing)
items <- grep( "R31" , colnames(data.pirlsmissing) , value=TRUE )
dat <- data.pirlsmissing
#****
# Model 1: recode missing responses as missing (missing are ignorable)
# data recoding
dat1 <- dat
dat1[ dat1 == 9 ] <- NA
# estimate Rasch model
mod1 <- rasch.mml2( dat1[,items] , weights= dat$studwgt , group=dat$country )
summary(mod1)
## Mean= 0 0.341 -0.134 0.219
## SD= 1.142 1.166 1.197 0.959
#****
# Model 2: recode missing responses as wrong
# data recoding
dat2 <- dat
dat2[ dat2 == 9 ] <- 0
# estimate Rasch model
mod2 <- rasch.mml2( dat2[,items] , weights= dat$studwgt , group=dat$country )
summary(mod2)
## Mean= 0 0.413 -0.172 0.446
## SD= 1.199 1.263 1.32 0.996
#****
# Model 3: recode missing responses as rho * P_i( theta ) and
# apply pseudo-log-likelihood estimation
# Missing item responses are predicted by the model implied probability
# P_i( theta ) where theta is the ability estimate when ignoring missings (Model 1)
# and rho is an adjustment parameter. rho=0 is equivalent to Model 2 (treating
# missing as wrong) and rho=1 is equivalent to Model 1 (treating missing as ignorable).
# data recoding
dat3 <- dat
# simulate theta estimate from posterior distribution
theta <- rnorm( nrow(dat3) , mean = mod1$person$EAP , sd=mod1$person$SE.EAP )
rho <- .3 # define a rho parameter value of .3
for (ii in items){
ind <- which( dat[,ii] == 9 )
dat3[ind,ii] <- rho*plogis( theta[ind] - mod1$item$b[ which( items == ii ) ] )
}
# estimate Rasch model
mod3 <- rasch.mml2( dat3[,items] , weights= dat$studwgt , group=dat$country )
summary(mod3)
## Mean= 0 0.392 -0.153 0.38
## SD= 1.154 1.209 1.246 0.973
#****
# Model 4: simulate missing responses as rho * P_i( theta )
# The definition is the same as in Model 3. But it is now assumed
# that the missing responses are 'latent responses'.
set.seed(789)
# data recoding
dat4 <- dat
# simulate theta estimate from posterior distribution
theta <- rnorm( nrow(dat4) , mean = mod1$person$EAP , sd=mod1$person$SE.EAP )
rho <- .3 # define a rho parameter value of .3
for (ii in items){
ind <- which( dat[,ii] == 9 )
p3 <- rho*plogis( theta[ind] - mod1$item$b[ which( items == ii ) ] )
dat4[ ind , ii ] <- 1*(runif( length(ind) , 0 , 1 ) < p3)
}
# estimate Rasch model
mod4 <- rasch.mml2( dat4[,items] , weights= dat$studwgt , group=dat$country )
summary(mod4)
## Mean= 0 0.396 -0.156 0.382
## SD= 1.16 1.216 1.253 0.979
#****
# Model 5: recode missing responses for multiple choice items with four alternatives
# to 1/4 and apply pseudo-log-likelihood estimation.
# Missings for constructed response items are treated as incorrect.
# data recoding
dat5 <- dat
items_mc <- items[ substring( items , 7,7) == "M" ]
items_cr <- items[ substring( items , 7,7) == "C" ]
for (ii in items_mc){
ind <- which( dat[,ii] == 9 )
dat5[ind,ii] <- 1/4
}
for (ii in items_cr){
ind <- which( dat[,ii] == 9 )
dat5[ind,ii] <- 0
}
# estimate Rasch model
mod5 <- rasch.mml2( dat5[,items] , weights= dat$studwgt , group=dat$country )
summary(mod5)
## Mean= 0 0.411 -0.165 0.435
## SD= 1.19 1.245 1.293 0.995
#*** For the following analyses, we ignore sample weights and the
# country grouping.
data(data.pirlsmissing)
items <- grep( "R31" , colnames(data.pirlsmissing) , value=TRUE )
dat <- data.pirlsmissing
dat1 <- dat
dat1[ dat1 == 9 ] <- 0
#*** Model 6: estimate item difficulties assuming incorrect missing data treatment
mod6 <- rasch.mml2( dat1[,items] , mmliter=50 )
summary(mod6)
#*** Model 7: reestimate model with constrained item difficulties
I <- length(items)
constraints <- cbind( 1:I , mod6$item$b )
mod7 <- rasch.mml2( dat1[,items] , constraints=constraints , mmliter=50 )
summary(mod7)
#*** Model 8: score all missings responses as missing items
dat2 <- dat[,items]
dat2[ dat2 == 9 ] <- NA
mod8 <- rasch.mml2( dat2 , constraints=constraints , mmliter=50 , mu.fixed=NULL )
summary(mod8)
#*** Model 9: estimate missing data model 'missing1' assuming a missingness
# parameter delta.miss of zero
dat2 <- dat[,items] # note that missing item responses must be defined by 9
mod9 <- rasch.mml2( dat2 , constraints=constraints , irtmodel="missing1" ,
theta.k=seq(-5,5,len=10) , delta.miss= 0 , mitermax= 4 , mmliter=200 ,
mu.fixed=NULL )
summary(mod9)
#*** Model 10: estimate missing data model with a large negative missing delta parameter
# => This model is equivalent to treating missing responses as wrong
mod10 <- rasch.mml2( dat2 , constraints=constraints , irtmodel="missing1" ,
theta.k=seq(-5 , 5 , len=10) , delta.miss= -10 , mitermax= 4 , mmliter=200 ,
mu.fixed=NULL )
summary(mod10)
#*** Model 11: choose a missingness delta parameter of -1
mod11 <- rasch.mml2( dat2 , constraints=constraints , irtmodel="missing1" ,
theta.k=seq(-5 , 5 , len=10) , delta.miss= -1 , mitermax= 4 ,
mmliter=200 , mu.fixed=NULL )
summary(mod11)
#*** Model 12: estimate delta parameter
mod12 <- rasch.mml2( dat2 , constraints=constraints , irtmodel="missing1" ,
theta.k=seq(-5 , 5 , len=10) , delta.miss= 0 , mitermax= 4 ,
mmliter=200 , est.delta=TRUE , mu.fixed=NULL )
summary(mod12)Run the code above in your browser using DataLab