tif {irtoys}

Test information function

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: the output of est.

x

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.

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))