TAM (version 0.04-43)

tam.ctt: Classical Test Theory Based Statistics

Description

This function computes some item statistics based on classical test theory.

Usage

tam.ctt(resp, wlescore=NULL, pvscores=NULL, group=NULL , progress=TRUE)

Arguments

resp

A data frame with unscored or scored item responses

wlescore

A vector with person parameter estimates, e.g. weighted likelihood estimates obtained from tam.wle

pvscores

A matrix with plausible values, e.g. obtained from tam.pv

group

Vector of group identifiers if descriptive statistics shall be groupwise calculated

progress

Display progress?

Value

• A data frame with following columns:
• index
  Index variable in this data frame
• group
  Group identifier
• itemno
  Item number
• item
  Item
• N
  Number of students responding to this item
• Categ
  Category label
• AbsFreq
  Absolute frequency of category
• RelFreq
  Relative frequency of category
• rpb.WLE
  Point biserial correlation of an item category and the WLE
• M.WLE
  Mean of the WLE of students in this item category
• SD.WLE
  Standard deviation of the WLE of students in this item category
• rpb.PV
  Point biserial correlation of an item category and the PV
• M.PV
  Mean of the PV of students in this item category
• SD.PV
  Standard deviation of the PV of students in this item category

Examples

#################################################
# Example data.mc
data(data.mc)
# estimate Rasch model for scored data.mc data
mod <- tam.mml( resp=data.mc$scored )
# estimate WLE
w1 <- tam.wle( mod )
# estimate plausible values
set.seed(789)
p1 <- tam.pv( mod , ntheta=500 , normal.approx=TRUE )$pv

# CTT results for raw data
stat1 <- tam.ctt( resp=data.mc$raw , wlescore=w1$theta , pvscores=p1[,-1] )

# CTT results for scored data
stat2 <- tam.ctt( resp=data.mc$scored , wlescore=w1$theta , pvscores=p1[,-1] )

# descriptive statistics for different groups
# define group identifier
group <- c( rep(1,70) , rep(2,73) )
stat3 <- tam.ctt( resp=data.mc$raw , wlescore=w1$theta , pvscores=p1[,-1] , group=group)