# NOT RUN {
#############################################################################
# EXAMPLE 1: Constructing sequential pseudo items for data.mg
#############################################################################
data(data.mg, package="CDM")
dat <- data.mg
items <- colnames(dat)[ which( substring( colnames(dat),1,1)=="I" ) ]
## [1] "I1" "I2" "I3" "I4" "I5" "I6" "I7" "I8" "I9" "I10" "I11"
data <- dat[,items]
# construct sequential dichotomous pseudo items
res <- CDM::sequential.items(data)
# item information table
res$iteminfo
## item itemindex category pseudoitem
## 1 I1 1 1 I1
## 2 I2 2 1 I2
## 3 I3 3 1 I3
## 4 I4 4 1 I4_Cat1
## 5 I4 4 2 I4_Cat2
## 6 I5 5 1 I5_Cat1
## 7 I5 5 2 I5_Cat2
## [...]
# extract dataset with pseudo items
dat.expand <- res$dat.expand
colnames(dat.expand)
## [1] "I1" "I2" "I3" "I4_Cat1" "I4_Cat2" "I5_Cat1"
## [7] "I5_Cat2" "I6_Cat1" "I6_Cat2" "I7_Cat1" "I7_Cat2" "I7_Cat3"
## [13] "I8" "I9" "I10" "I11_Cat1" "I11_Cat2" "I11_Cat3"
# compare original items and pseudoitems
#**** Item I1
stats::xtabs( ~ paste(data$I1) + paste(dat.expand$I1) )
## paste(dat.expand$I1)
## paste(data$I1) 0 1 NA
## 0 4339 0 0
## 1 0 33326 0
## NA 0 0 578
#**** Item I7
stats::xtabs( ~ paste(data$I7) + paste(dat.expand$I7_Cat1) )
## paste(dat.expand$I7_Cat1)
## paste(data$I7) 0 1 NA
## 0 3825 0 0
## 1 0 14241 0
## 2 0 14341 0
## 3 0 5169 0
## NA 0 0 667
stats::xtabs( ~ paste(data$I7) + paste(dat.expand$I7_Cat2) )
## paste(dat.expand$I7_Cat2)
## paste(data$I7) 0 1 NA
## 0 0 0 3825
## 1 14241 0 0
## 2 0 14341 0
## 3 0 5169 0
## NA 0 0 667
stats::xtabs( ~ paste(data$I7) + paste(dat.expand$I7_Cat3) )
## paste(dat.expand$I7_Cat3)
## paste(data$I7) 0 1 NA
## 0 0 0 3825
## 1 0 0 14241
## 2 14341 0 0
## 3 0 5169 0
## NA 0 0 667
# }
# NOT RUN {
#*** Model 1: Rasch model for sequentially created pseudo items
mod <- CDM::gdm( dat.expand, irtmodel="1PL", theta.k=seq(-5,5,len=21),
skillspace="normal", decrease.increments=TRUE)
# }
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