tif: Test information function

In lebebr01/irtoys-2: Simple interface to the estimation and plotting of IRT models

Description

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.

Usage

  tif(ip, x = NULL)

Arguments

ip	Item parameters: a matrix with one row per item, and three columns: [,1] item discrimination a, [,2] item difficulty b, and [,3] asymptote c.
x	The values of the latent variable (θ 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.

Details

A common use of this function would be to obtain a plot of the TIF.

Value

A list of:

x	A copy of the argument x
f	A vector containing the TIF values

Author(s)

Ivailo Partchev

See Also

plot.tif, iif

Examples

plot(trf(Scored2pl$est))

lebebr01/irtoys-2 documentation built on May 20, 2019, 11:29 p.m.