iff {pairwise}

Item information function

Description

plotting function for plotting the Item information function(IIF).

Usage

iff(
  pair_obj,
  itemnumber = 1,
  x = NULL,
  plot = TRUE,
  cat = FALSE,
  lwd = 2,
  col = 1,
  ...
)

Arguments

pair_obj

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

itemnumber

an integer, defining the number of the item to plot the respective item information function for. This is set to an arbitrary default value of itemnumber = 1 to avoid error messages when you forget to choose an item to plot the item information function for.

x

The value(s) of the latent variable, at which the IIF 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.

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 or return the values of the Item information function based on item categories.

lwd

see parameters for plot

col

see parameters for plot

...

arguments passed to plot

Details

no details in the moment.

Value

a plot, a matrix or a single numeric with values of the Item information function.

Examples

########
data(sim200x3)
result <- pair(sim200x3)
# IFF plot for Item No. 2 
iff(pair_obj = result, itemnumber = 2 ) 
# IFF plot for Categories of Item No. 2
iff(pair_obj = result, itemnumber = 2 ,cat=TRUE)
# IFF at theta=0 for Item No. 2 
iff(pair_obj = result, itemnumber = 2 ,x=0) 
# IFF at theta=0 for Categories of Item No. 2
iff(pair_obj = result, itemnumber = 2 ,x=0,cat=TRUE)
# IFF of Item No. 2 for a given range of thetas 
iff(pair_obj = result, itemnumber = 2 ,x=seq(0,4,.1)) 
# ... etc.
iff(pair_obj = result, itemnumber = 2 ,x=seq(0,4,.1),cat=TRUE) 
##### examples with other data ...
data(bfiN)
result <- pair(bfiN)
iff(pair_obj = result, itemnumber = 3 )
iff(pair_obj = result, itemnumber = 3 ,cat=TRUE)