tff {pairwise}

Test information function

Description

plotting function for plotting the test information function (TIF).

Usage

tff(
  pair_obj,
  items = NULL,
  x = NULL,
  main = "Test Information Function",
  plot = TRUE,
  cat = FALSE,
  lwd = 2,
  col = 1,
  ...
)

Arguments

pair_obj

an object of class "pair" as a result from function pair.

items

optional a vector (character or numeric) identifying the items (according their order in the data) to use for plotting the test information function.

x

The value(s) of the latent variable, at which the TIF will be evaluated. x should be either a numeric vector of theta values or a single numeric value. If x is given as a single numeric value plotting is supressed. If not given (default), 99 values spaced evenly between -4 and +4 will be used, handy for plotting.

main

see parameters for plot

plot

a logical (default plot = TRUE), defining wether to supress plotting an just return a matrix of the values of the Item information function.

cat

a logical (default cat = FALSE), defining wether to plot as an overlay to the Test information function the item category information functions based on item categories. If cat = TRUE and plot = FALSE the values of the item category information functions are returned.

lwd

see parameters for plot

col

see parameters for plot

...

arguments passed to plot

Details

no details in the moment.

Value

a plot, a "data.frame" or a single numeric with values of the Test information function.

Examples

########
data(sim200x3)
result <- pair(sim200x3)
tff(pair_obj = result) # TIF plot 
tff(pair_obj = result, cat=TRUE) # TIF plot 
tff(pair_obj = result, items=c("V1","V3"), cat=TRUE) # TIF plot 
tff(pair_obj = result, x=0) # TIF at theta=0 
tff(pair_obj = result, x=seq(0,4,.1)) # TIF for a given range of Thetas
##### examples with other data ...
data(bfiN)
result <- pair(bfiN)
tff(pair_obj = result)
tff(pair_obj = result, cat=TRUE) # TIF plot