Item parameters: a matrix with one row per
  item, and three columns: [,1] item discrimination
  $a$, [,2] item difficulty $b$, and [,3] asymptote
  $c$.

The values of the latent variable ($\theta$
  in the equation above), at which the TIF will be
  evaluated. If not given, 99 values spaced evenly between
  -4 and +4 will be used, handy for plotting.


  Returns the test information function (TIF) of the 3PL
  (1PL, 2PL) model. The TIF is the sum of the item
  information functions (IIF) in a test, and indicates the
  precision of measurement that can be achieved with the
  test at any value of the latent variable, bein inversely
  related to measurement variance.


models

Provides a simple common interface to the estimation of item
parameters in IRT models for binary responses with three different programs
(ICL, BILOG-MG, and ltm, and a variety of functions useful with IRT models.

tif: Test information function

Description

Usage

Arguments

Value

Details

See Also

Examples